Room Thermostat Slimline V4

Heatmiser Room Thermostat Slimline V4

The Heatmiser Slimline V4 is a programmable room thermostat designed to control heating systems according to selected temperatures and daily schedules. It combines room temperature regulation, programmable heating periods, manual temperature adjustment, and timer functions in a wall-mounted unit.

The Slimline V4 supports two operating modes: Programmable Thermostat (Mode 01) and Time Clock (Mode 02). Thermostat Mode controls heating according to the selected temperature, while Time Clock Mode switches a compatible electrical output according to programmed ON and OFF periods.

The thermostat features a large LCD screen, six control buttons, temperature hold, holiday programming, frost protection, keypad locking, optional floor temperature sensing, and adjustable heating settings. It supports Weekday/Weekend (5/2 Day), 7 Day, and 24 Hour programming.In Time Clock Mode, the Slimline V4 can control compatible equipment such as hot water systems, towel rails, and lighting. A separate Countdown Mode is also available for timed output operation.

The thermostat operates using a 230V AC supply and supports switched-live boiler, volt-free boiler, and spring-return heating valve connections.

Product Overview and Technical Specifications

The Heatmiser Slimline V4 is part of the Heatmiser Slimline Series and provides programmable heating control with an alternative time clock operating mode.

How the Programmable Room Thermostat Works

The Slimline V4 combines a heating programmer and a room thermostat.

The thermostat measures the room temperature and requests heating when the measured temperature falls below the selected target. Once the required temperature is reached, heating demand stops.

The programming function allows different temperatures to be maintained at selected times throughout the day.

Understanding Temperature Settings

Increasing the target temperature does not cause the heating system to warm a room faster. The heating speed depends on the system’s design and capacity.

A higher target temperature causes heating to continue until the higher temperature is reached.

Similarly, reducing the target temperature does not make a room cool faster. It changes the temperature that the thermostat maintains.

Choosing a Comfortable Room Temperature

A practical method of finding a suitable heating temperature is to start at approximately 18°C and increase the setting by 1°C each day until the required comfort level is reached.

Once a comfortable temperature has been established, the programmed schedule can maintain it automatically.

Avoiding unnecessarily high settings helps reduce heating energy consumption.

Using Thermostatic Radiator Valves

In heating systems with a boiler and radiators, one programmable room thermostat may control the heating for the entire house.

Thermostatic radiator valves (TRVs) can provide additional temperature control in individual rooms.

When TRVs are installed, the main room thermostat can be set to provide a comfortable temperature throughout the property while the radiator valves limit heating in individual rooms.

Thermostat Placement and Airflow

The thermostat requires unrestricted airflow to measure the surrounding temperature accurately.

It should not be covered by curtains or obstructed by furniture.

Nearby electrical heaters, televisions, wall lamps, and table lamps can interfere with temperature measurement.

Parts, Components, and Control Buttons

The Heatmiser Slimline V4 has a large LCD display above six control buttons.

The front panel contains the operating controls, while the back plate provides the mounting and electrical connection arrangement.

Main Components

Control Button Functions

Some functions require a button to be pressed more than once or held together with another button.

Understanding the LCD Display

The Slimline V4 displays the measured temperature, current day, clock, heating demand, and operating status.

The displayed information changes according to the selected operating mode.

Thermostat Mode Display Indicators

Flame Icon

The flame icon appears when heating is requested.

When the flame icon is absent, the thermostat does not currently need heating to maintain the selected temperature.

The flame icon flashes when Optimum Start is active.

Floor Temperature Limit Icon

The floor temperature limit icon appears when the connected floor probe reaches the configured maximum floor temperature.

Keypad Lock Icon

The keypad lock indicator appears only while the keypad is locked.

Safety Instructions and Installation Requirements

The Heatmiser Slimline V4 operates using a 230V AC electrical supply.

Installation must be completed by a qualified electrician and comply with applicable local electrical regulations.

Important Installation Precautions

• Mount the thermostat at eye level.
• Read the operating instructions before installation.
• Do not install the thermostat near a direct heat source.
• Do not apply excessive pressure to the LCD screen because permanent damage may occur.
• Use a recessed wall back box with a minimum depth of 35 mm.
• Follow the correct wiring diagram for the connected heating equipment.
• The manufacturer’s volt-free boiler and spring-return valve diagrams specify protection by a fuse or RCD.

Electrical Installation

The thermostat must be connected according to the wiring arrangement required by the connected boiler or heating valve.

The boiler manufacturer’s wiring instructions must also be followed.

Temperature Sensor Precautions

The thermostat supports different air and floor sensor configurations.

When both sensors are used, the floor probe acts as a temperature-limiting sensor to help protect against excessive floor temperature.

Installing the Heatmiser Slimline V4

The Slimline V4 is designed for flush mounting into a recessed wall back box.

A minimum box depth of 35 mm is required.

Step 1: Remove the Front Panel

1. Locate the slots along the bottom face of the thermostat.
2. Insert a small flat-head terminal screwdriver into the slots.
3. Carefully separate the front panel from the back plate.
4. Place the front panel somewhere safe.

Step 2: Connect the Electrical Wiring

The thermostat wiring must follow the appropriate manufacturer’s diagram.

The manual provides connection arrangements for:

• Switched-live boiler control.
• Volt-free boiler control.
• Spring-return heating valve control.

The electrical connections must match the installed heating equipment.

Step 3: Mount the Back Plate

1. Position the back plate against the recessed back box.
2. Align the fixing holes.
3. Screw the back plate securely into place.

Step 4: Reattach the Front Panel

1. Align the front panel with the mounted back plate.
2. Carefully clip the front section into position.
3. Check that the panel is properly seated on the back plate.

Selecting Thermostat or Time Clock Mode

The Slimline V4 supports two operating modes.

Programmable Thermostat Mode is the factory default.

Mode 01: Programmable Thermostat

This mode controls heating according to temperature settings and programmed comfort levels.

It supports manual temperature adjustments, Temperature Hold, Holiday Mode, Frost Protection, and compatible temperature sensors.

Mode 02: Time Clock

This mode controls a timed output according to programmed ON and OFF periods.

It can be used with compatible equipment such as hot water systems, towel rails, and lighting.

How to Change the Operating Mode

1. Press and hold Power to turn off the display.
2. Press and hold Power and Up together.
3. Continue holding until the LCD powers up.
4. All display icons appear momentarily.
5. The thermostat performs a factory reset and displays the operating mode options.
6. Use Up or Down to select the required mode.
7. Select 01 for Programmable Thermostat or 02 for Time Clock.
8. Press A to confirm.
9. Press Power to turn the display on.

Important: Changing the operating mode performs a factory reset and restores the device’s configuration to its default settings.

Mode 1: Programmable Thermostat Operation

Programmable Thermostat Mode controls heating according to measured temperature and the selected heating schedule.

The available functions include:

• Room temperature control.
• Floor temperature monitoring.
• Programmable heating schedules.
• Manual temperature adjustment.
• Temperature Hold.
• Holiday Mode.
• Frost Protection.
• Keypad locking.
• Optimum Start.
• Temperature sensor selection.
• Advanced heating settings.

Setting the Clock

The clock must be set correctly for the programmed heating schedule to operate at the required times.

How to Set the Clock in Programmable Mode

1. Make sure the thermostat is turned on.
2. Press Clock twice.
3. Use Up and Down to set the hour.
4. Press H to confirm.
5. Use Up and Down to set the minutes.
6. Press H.
7. Use Up and Down to select the current day of the week.
8. Press A to save the settings and return to the main display.

The clock uses a 24-hour time format.

Note: When Feature 11 is set to Manual Mode, the Clock button does not respond.

Room and Floor Temperature Display

The Slimline V4 can be configured to use an air sensor, floor sensor, or both.

The LCD identifies the active temperature reading as ROOM TEMP or FLOOR TEMP.

Room Temperature

When room temperature is displayed, ROOM TEMP appears beside the measured value.

Floor Temperature

When floor temperature is displayed, FLOOR TEMP appears beside the measured value.

Combined Air and Floor Sensing

When both sensors are enabled, the room temperature is displayed by default.

The connected floor probe can provide temperature limiting.

How to View the Floor Temperature

1. Press and hold the A button.
2. Continue holding until the floor temperature appears.
3. The display shows FLOOR TEMP with the measured value.

Heating Programs and Comfort Levels

The Slimline V4 supports three heating schedule arrangements.

Available Programming Modes

The programming mode is selected through Feature 10.

Comfort Periods

The four comfort periods are:

5/2 Day Programming

This mode provides separate schedules for weekdays and weekends.

Four comfort levels apply to Monday through Friday, while another four can be programmed for Saturday and Sunday.

7 Day Programming

In 7 Day Mode, every day can have its own four programmed comfort levels.

24 Hour Programming

In 24 Hour Mode, the same four comfort periods apply every day.

Programming the Heating Comfort Levels

The heating schedule is configured using the Clock, H, A, and Up/Down buttons.

How to Program Comfort Levels

1. Press Clock once.
2. The display identifies the day or day group being programmed.
3. Use Up and Down to set the required WAKE starting time.
4. Press H to confirm.
5. Use Up and Down to set the WAKE temperature.
6. Press H to confirm.
7. LEAVE appears on the display.
8. Repeat the time and temperature settings for LEAVE.
9. Continue configuring RETURN and SLEEP.
10. Press A to save the program and return to the main display.

Day Display During Programming

The day indicator changes according to the selected programming mode.

Programming Weekends in 5/2 Day Mode

After setting the weekday comfort levels, Saturday and Sunday appear.

The weekend comfort periods can then be programmed separately.

Programming Individual Days

In 7 Day Mode, the programming process can be repeated for each day independently.

Disabling Unused Comfort Periods

If a comfort period is not required, its time can be set to –:–.

The thermostat ignores that period and continues to the next scheduled level.

Adjusting the Set Temperature

The Up and Down buttons allow the target temperature to be changed directly.

How to Change the Temperature

1. Press Up or Down.
2. SET appears with the selected target temperature.
3. Use Up and Down to adjust the temperature.
4. Press A to confirm and return to the main display.

Temperature Adjustment in Programmable Mode

When the thermostat is following a programmed heating schedule, the manually selected temperature remains active until the next comfort period begins.

At that time, the thermostat returns to the programmed temperature.

Temperature Adjustment in Manual Mode

When the thermostat is configured as non-programmable, the selected temperature is maintained continuously.

Temperature Hold Function

Temperature Hold temporarily overrides the programmed heating schedule.

It allows a different temperature to be maintained for a selected duration.

How to Activate Temperature Hold

1. Press H.
2. Use Up and Down to select the required hold duration.
3. Press H to confirm.
4. Use Up and Down to select the required hold temperature.
5. Press A to save the settings.

HOLD FOR appears on the display with the remaining hold time.

When the countdown reaches zero, the thermostat returns to its normal programmed schedule.

How to Cancel Temperature Hold

1. Press H to open the hold settings.
2. Reduce the hold duration to 00:00.
3. Confirm the setting.

The temporary hold is canceled.

Locking and Unlocking the Thermostat

The Slimline V4 includes a keypad lock.

How to Lock the Keypad

1. Press and hold A and Down together.
2. Continue holding for 10 seconds.
3. The keypad lock symbol appears.

The keypad is now locked.

How to Unlock the Keypad

1. Press and hold A and Down together again.
2. Continue holding for 10 seconds.
3. The keypad lock symbol disappears.

The keypad is unlocked.

Keypad Lock Indicator

The lock symbol appears only while the keypad lock is active.

Holiday Mode

Holiday Mode temporarily reduces the heating temperature to the configured frost protection setting.

The thermostat maintains that reduced temperature throughout the holiday period and automatically returns to the programmed schedule when the holiday ends.

How to Activate Holiday Mode

1. Press H three times.
2. Continue until the suitcase symbol appears.
3. Use Up and Down to select the required number of holiday days.
4. Press A to confirm.

The suitcase symbol remains displayed while Holiday Mode is active.

When Does Holiday Mode Start?

The holiday does not begin until 00:00 on the following day.

For example, when a two-day holiday is configured on Friday:

• Saturday is counted as the first holiday day.
• Sunday is counted as the second holiday day.
• The thermostat returns to the programmed schedule at 00:00 on Monday.

How to Cancel Holiday Mode

1. Open the Holiday settings by pressing H three times.
2. Reduce the holiday duration to 00 days.
3. Press A to confirm.

Holiday Mode is canceled.

Frost Protection Mode

Frost Protection maintains a reduced temperature when normal heating is not required.

How to Activate Frost Protection

1. Press Power once.
2. The frost protection symbol appears.

The thermostat requests heating only when the measured room temperature falls below the configured frost temperature.

If heating becomes active, the flame symbol appears.

How to Cancel Frost Protection

Press Power once again.

The frost protection symbol disappears.

Frost Protection Temperature Settings

Frost Protection When the Display Is Off

The thermostat includes an optional setting that determines whether frost protection remains enabled while the main display is off.

This function is controlled by Feature 03.

The factory default keeps frost protection enabled when the display is off.

If the thermostat requests heating with its display switched off, the frost symbol represents the heating demand.

Turning the Heating On and Off

The flame icon identifies when the thermostat is requesting heating.

When the flame icon disappears, the thermostat remains active but does not currently require heat.

How to Turn the Thermostat Off

1. Press and hold Power.
2. Continue until the display switches off.

The display and normal heating output are switched off, subject to the configured frost protection behavior.

How to Turn the Thermostat On

Press Power once.

The thermostat returns to its normal operating display.

Power Off and Frost Protection

Feature 03 determines whether frost protection remains available with the display switched off.

When this feature is enabled, the thermostat can still request heating for frost protection.

When disabled, the thermostat does not maintain frost protection while switched off.

Advanced Thermostat Settings

The Slimline V4 provides optional features for temperature control, sensor selection, floor temperature limiting, and programming.

Most settings can remain at their factory defaults.

How to Access the Optional Features

1. Press and hold Power to turn off the thermostat.
2. Press and hold Clock.
3. Continue until the optional feature screen appears.
4. Use Clock to move through the available features.
5. Use Up and Down to change the selected setting.
6. Press A to confirm.
7. Press Power to turn the thermostat back on.

Optional Features Reference Table

Feature 01: Temperature Format

This feature changes the display between Celsius and Fahrenheit.

Feature 02: Switching Differential

Switching Differential determines how far the measured temperature must fall below the selected target before heating starts.

For example, with a target temperature of 20°C:

• A 1°C differential activates heating at 19°C and stops it at 20°C.
• A 2°C differential activates heating at 18°C and stops it at 20°C.

The range is 1–3°C.

The default is 1°C.

Feature 03: Frost Mode

This setting determines whether the thermostat maintains frost protection when its display is switched off.

Feature 04: Output Delay

Output Delay prevents rapid switching of the heating output.

The adjustable range is 0–15 minutes.

The default is 0 minutes, meaning no additional delay is applied.

Feature 05: Temperature Adjustment Limit

This feature restricts the amount of temperature adjustment available through Up and Down.

The restriction also applies while the keypad is locked, allowing limited control of the heating system.

The adjustable range is 0–10°C.

Feature 06: Sensor Selection

The thermostat supports five sensor configurations.

When both air and floor sensors are selected, the floor probe acts as a limiting sensor to help prevent excessive floor temperature.

Feature 07: Floor Temperature Limit

This feature sets the floor temperature limit when a floor probe is enabled.

The adjustable range is 20–45°C.

The factory default is 27°C.

When the measured floor temperature reaches the configured limit, the floor temperature limit symbol appears.

Feature 08: Optimum Start

Optimum Start calculates when heating should begin so that the programmed target temperature is reached at the required time.

The thermostat uses its calculated heating rate to determine the necessary warm-up period.

The adjustable range is 0–3 hours.

The default is 0, meaning Optimum Start is disabled.

Feature 09: Rate of Change

Rate of Change represents the number of minutes the thermostat calculates are required to raise the room temperature by 1°C.

For example, a rate of 20 indicates an estimated 20 minutes for a 1°C temperature increase.

The thermostat continues monitoring the heating system’s performance to update the calculated heating rate.

Feature 10: Programming Mode

The programming mode determines how heating comfort levels are assigned throughout the week.

Feature 11: Thermostat Mode

This feature selects manual or programmable temperature control.

When Manual Mode is selected, the thermostat maintains the selected temperature without following scheduled comfort levels.

The Clock button does not respond in Manual Mode.

Recalibrating the Thermostat

The Slimline V4 includes a temperature recalibration function.

How to Recalibrate

1. Press and hold Power to turn off the display.
2. Press and hold Power and Down together.
3. Continue until the calibration temperature appears.
4. Use Up and Down to select the required temperature value.
5. Press A to confirm.
6. Press Power to turn the thermostat on.

The thermostat then uses the adjusted calibration setting.

Error Codes and Troubleshooting

The Slimline V4 displays error codes when a temperature sensor fault is detected.

Error Code Reference

Error E0: Internal Sensor Fault

E0 indicates that the internal temperature sensor has developed a fault.

The manufacturer advises contacting the thermostat retailer for assistance.

Error E1: Remote Floor Probe Fault

E1 indicates a problem with the remote floor sensor.

Possible conditions include:

• The floor probe is disconnected.
• The floor probe is incorrectly wired.
• The floor probe is faulty.

The sensor and its connections require checking by an appropriate qualified professional.

Error E2: Remote Air Probe Fault

E2 indicates a problem with the remote air temperature sensor.

Possible conditions include:

• The remote air probe is disconnected.
• The remote air probe is incorrectly wired.
• The remote air probe is faulty.

The sensor and its connections require checking by an appropriate qualified professional.

Common Operating Problems and Checks

Checking an Unexpected Heating Schedule

When heating does not follow the expected schedule:

1. Check the current clock and day settings.
2. Review the programmed comfort levels.
3. Check the selected programming mode.
4. Check whether Temperature Hold is active.
5. Check whether Holiday or Frost Protection Mode is active.
6. Check whether Feature 11 is set to Manual Mode.

Checking Floor Temperature Settings

When the floor limit symbol appears, the configured maximum floor temperature has been reached.

Feature 07 controls the temperature limit, and Feature 06 selects the active sensors.

Mode 2: Time Clock Operation

The Slimline V4 can operate as a programmable time clock.

In this mode, the output is controlled according to switching times rather than measured room temperature.

The manufacturer identifies applications such as:

• Hot water systems.
• Towel rails.
• Lighting.

The connected equipment manufacturer’s wiring instructions must be followed.

Time Clock LCD Display

The display changes when the Slimline V4 operates in Time Clock Mode.

Time Clock Display Indicators

Setting the Clock in Time Clock Mode

The time clock uses different button sequences depending on whether Countdown Mode or a programmed switching schedule is selected.

How to Set the Time

1. In Countdown Mode, press Clock once.
2. In 5/2 Day, 7 Day, or 24 Hour Mode, press Clock twice.
3. Use Up and Down to set the hours.
4. Press H to confirm.
5. Use Up and Down to set the minutes.
6. Press H.
7. Use Up and Down to select the day of the week.
8. Press A to save the settings.

Time Clock Programming Modes

Time Clock Mode supports three scheduled programming arrangements and a separate countdown setting.

The scheduled switching mode is configured through Feature 01.

Feature 02 selects Countdown or Programmable Time Clock operation.

Programming Time Clock Switching Times

The Slimline V4 supports four ON/OFF switching periods per programmed day or day group.

These periods are identified as WAKE, LEAVE, RETURN, and SLEEP.

Switching Periods

How to Set the Switching Times

1. Press Clock once.
2. The display shows the day or day group according to the selected programming mode.
3. Use Up and Down to set the TIMER ON time for WAKE.
4. Press H to confirm.
5. Use Up and Down to set the TIMER OFF time for WAKE.
6. Press H.
7. Repeat the procedure for LEAVE, RETURN, and SLEEP.
8. In 5/2 Day Mode, Saturday and Sunday appear after the weekday settings.
9. Configure the weekend switching periods as required.
10. Press A to save the settings.

Day Display During Programming

Disabling Unused Switching Periods

An unused switching period can be disabled by setting its time to –:–.

The time clock ignores the disabled period.

Countdown Mode

Countdown Mode activates the timed output for a selected duration.

How to Use Countdown Mode

1. Use Up and Down to select the required countdown duration.
2. Press A to confirm.
3. HOLD FOR appears on the display.
4. The remaining countdown duration is shown.

The timed output remains active while HOLD FOR is displayed.

How to Cancel the Countdown

Reduce the countdown duration to 00:00.

The countdown is canceled.

Countdown Display Indicators

Timer Override

Timer Override temporarily changes the current output state without editing the switching schedule.

How to Override the Timer

When the time clock currently displays TIMER ON:

1. Press A.
2. The time clock changes the output to TIMER OFF.
3. TIMER OFF flashes to indicate that the programmed output has been overridden.

The time clock returns to its normal switching schedule at the next programmed time.

Locking and Unlocking the Time Clock

The Slimline V4 also supports keypad locking in Time Clock Mode.

How to Lock the Time Clock

1. Press and hold A and Down together.
2. Continue holding for 10 seconds.
3. The keypad lock symbol appears.

How to Unlock the Time Clock

1. Press and hold A and Down together again.
2. Continue holding for 10 seconds.
3. The keypad lock symbol disappears.

Holiday Mode in Time Clock Operation

Holiday Mode keeps the timed output off for a selected number of days.

At the end of the holiday period, the time clock automatically returns to its programmed switching schedule.

How to Activate Holiday Mode

1. Press H once.
2. The suitcase symbol appears.
3. Use Up and Down to enter the required number of holiday days.
4. Press A to confirm.

The suitcase symbol remains displayed during the holiday.

When Does the Holiday Begin?

The holiday period begins at 00:00 on the following day.

For example, when a two-day holiday is configured on Friday, Saturday and Sunday are the holiday days.

Normal programmed operation resumes at 00:00 on Monday.

How to Cancel Holiday Mode

1. Press H to open the holiday setting.
2. Reduce the duration to 00 days.
3. Press A to confirm.

Advanced Time Clock Settings

The Time Clock Mode includes two optional features.

Time Clock Optional Features

Feature 01: Programming Mode

This setting selects the scheduled switching arrangement.

The default is 5/2 Day.

Feature 02: Time Clock Mode

This setting selects whether the unit operates as a countdown timer or a programmable time clock.

How to Change Time Clock Settings

1. Press and hold Power to switch off the time clock.
2. Press and hold Clock until the optional feature screen appears.
3. Use Clock to move between features.
4. Use Up and Down to change the selected setting.
5. Press A to confirm.
6. Press Power to return to normal operation.

Electrical Wiring Diagrams

The Slimline V4 includes electrical wiring diagrams for three heating control arrangements.

The manufacturer specifies that the thermostat operates from a 230V AC, 50/60 Hz supply.

The thermostat must only be installed by a qualified electrician, and the installation must comply with local electrical regulations.

Wiring Terminal Identification

The terminal strip is labeled:

RT2 — RT1 — – — A2 — A1 — N — L

The switching connection arrangement depends on the heating equipment being controlled.

Switched-Live Boiler Wiring

The switched-live boiler diagram shows the Slimline V4 connected to a boiler requiring a switched-live control signal.

Connections Shown

The manufacturer’s diagram identifies:

• 230V AC mains supply.
• Live connection to L.
• Neutral connection to N.
• Live link to the switching circuit.
• Switched-live output to the boiler.

Switched-Live Control

In the illustrated arrangement, A1 receives the live feed through a link from L, while A2 provides the switched-live output to the boiler.

The exact boiler connections must follow the boiler manufacturer’s wiring diagram.

Volt-Free Boiler Wiring

The volt-free boiler wiring diagram shows the thermostat connected to a boiler that requires a separate room thermostat switching contact.

The manufacturer specifies that this arrangement must be protected by a fuse or RCD.

Volt-Free Terminal Connections

Boiler LS and LR Terminals

The boiler connections are identified as LS and LR.

These are normally the boiler’s room thermostat terminals.

The thermostat receives its own mains supply through L and N, while A1 and A2 provide the separate control connection.

The manufacturer’s diagram must be followed for the installed boiler.

Spring-Return Heating Valve Wiring

The Slimline V4 can also be connected to a spring-return heating valve arrangement.

The manufacturer’s diagram shows the thermostat, heating valve, boiler control circuit, and optional remote air temperature probe.

Components Shown

• Slimline V4 thermostat.
• 230V AC power supply.
• Spring-return heating valve.
• Boiler room thermostat connections.
• Optional remote air temperature probe.
• Fuse or RCD protection.

Heating Valve Connections

The diagram shows a switched output from the thermostat controlling the heating valve.

The valve’s associated switching arrangement is connected to the boiler control circuit.

Boiler Connections

The diagram identifies the boiler room thermostat connections as LS and LR.

The boiler manufacturer’s wiring diagram must be consulted to determine the correct connections.

Optional Remote Air Sensor

The remote air sensor is shown connected through RT2 and the sensor common terminal.

The sensor configuration must be selected through Feature 06 to match the installed sensor.

Comparing the Wiring Arrangements

The wiring arrangement must be selected according to the installed heating system.

The electrical diagrams must be followed by a qualified electrician.

Factory Reset Instructions

The Slimline V4 includes a factory reset function within the operating mode selection procedure.

How to Factory Reset the Slimline V4

1. Press and hold Power to turn off the display.
2. Press and hold Power and Up together.
3. Continue until the LCD powers up.
4. All display icons appear momentarily.
5. The thermostat performs a factory reset.
6. The operating mode selection screen appears.
7. Use Up and Down to select Mode 01 or Mode 02.
8. Press A to confirm.
9. Press Power to turn the display on.

The thermostat restarts in the selected operating mode.

Selecting the Mode After Reset

After the reset, the required clock, programming, and optional settings can be configured again.

Customer Support and Manufacturer Information

Heatmiser provides technical support and additional product information through its official support channels.

Additional product information and technical specifications are available through the Heatmiser website.

Frequently Asked Questions

1. How is the Heatmiser Slimline V4 thermostat programmed?

Press Clock once to open the comfort level programming screen.

Use Up and Down to set the WAKE starting time, then press H to confirm. Select the WAKE temperature and press H again.

Repeat the process for LEAVE, RETURN, and SLEEP.

Press A to save the heating schedule.

The thermostat supports 5/2 Day, 7 Day, and 24 Hour programming.

2. How is the Heatmiser Slimline V4 factory reset?

Press and hold Power to turn off the display.

Press and hold Power and Up together until the LCD powers up and all display icons appear.

The thermostat performs a factory reset and displays Mode 01 and Mode 02.

Select the required operating mode using Up and Down, press A to confirm, and press Power to turn the thermostat on.

3. How is the Slimline V4 keypad unlocked?

Press and hold A and Down together for 10 seconds.

The keypad lock symbol disappears when the keypad is unlocked.

The same button combination is used to lock the thermostat.

4. What does E1 mean on the Heatmiser Slimline V4?

E1 indicates a problem with the remote floor temperature probe.

The probe may be disconnected, incorrectly wired, or faulty.

The floor sensor and its wiring should be checked by an appropriate qualified professional.

5. How is the Slimline V4 thermostat changed from Celsius to Fahrenheit?

Open the optional features menu by switching off the thermostat and holding Clock.

Select Feature 01.

Choose 00 for Celsius or 01 for Fahrenheit.

Press A to confirm, then press Power to return to normal operation.

6. What is the difference between Thermostat Mode and Time Clock Mode?

Thermostat Mode controls heating according to measured temperature and programmed comfort levels.

Time Clock Mode controls a compatible electrical output according to programmed ON and OFF times.

Time Clock Mode also includes Countdown operation for activating the output for a selected duration.

7. How is Holiday Mode activated on the Slimline V4?

In Thermostat Mode, press H three times until the suitcase symbol appears.

Use Up and Down to select the number of holiday days, then press A.

Holiday Mode begins at 00:00 on the following day and maintains the configured frost protection temperature.

In Time Clock Mode, press H once to configure Holiday Mode, which keeps the timed output off during the holiday period.

8. Why does the Slimline V4 thermostat not turn off the heating completely when the display is off?

Feature 03 controls whether frost protection remains active while the display is switched off.

The default setting keeps frost protection enabled, allowing heating demand when the temperature falls below the configured frost temperature.

To change this behavior, Feature 03 can be set to 01, which disables frost protection while the display is off.