Slimline-E V3 Electric Thermostat

Heatmiser Electric Underfloor Heating Thermostat

The Heatmiser Slimline-E V3 is a programmable thermostat designed to control electric underfloor heating systems. It combines temperature control, heating schedules, floor temperature monitoring, frost protection, and other settings in a wall-mounted unit with an LCD display.

The thermostat supports two operating modes: Programmable Thermostat Mode (Mode 01) and Time Clock Mode (Mode 02). Thermostat mode regulates heating according to temperature settings, while time clock mode controls connected equipment using programmed switching times or a countdown timer.

The Slimline-E V3 supports built-in air, remote air, and floor temperature sensors. For electric underfloor heating, the floor sensor must be used either independently or together with an air sensor.

This manual provides installation instructions, wiring information, thermostat programming steps, temperature control settings, holiday and frost protection functions, factory reset instructions, advanced settings, and error code information.

Product Overview

The Heatmiser Slimline-E V3 provides programmable heating control with several adjustable features for different operating requirements.

Understanding the Programmable Room Thermostat

A programmable room thermostat combines a temperature controller with a heating programmer.

The thermostat monitors temperature and activates heating when the measured temperature falls below the required setting. Heating stops when the selected temperature is reached.

The programming function allows different temperature settings to be applied at different times of the day and on different days of the week.

How Temperature Settings Affect Heating

Increasing the thermostat temperature does not make the heating system warm a room faster. Heating speed depends on the design and size of the heating system.

A higher set temperature causes the system to continue heating until the higher temperature is achieved.

Similarly, reducing the set temperature does not make a room cool faster. It changes the temperature that the thermostat will maintain.

Selecting a Comfortable Temperature

A practical way to establish a comfortable setting is to begin with a lower temperature, such as 18°C, and increase it gradually by 1°C each day until the desired comfort level is reached.

Once a suitable temperature has been established, the thermostat can maintain it according to the selected heating schedule.

Parts, Buttons, and Control Panel

The Heatmiser Slimline-E V3 has an LCD screen and six control buttons along the lower front panel.

Thermostat Control Buttons

The exact action depends on the selected operating mode and the screen currently displayed.

LCD Display Symbols and Indicators

The Slimline-E V3 LCD provides information about the current temperature, heating demand, active program, and operating status.

Thermostat Mode Display Indicators

The flame indicator is particularly useful for checking the heating demand.

When the flame icon is present, the thermostat is requesting heat. When it disappears, the thermostat has no current requirement for heating to maintain the selected temperature.

Installation Instructions

The Heatmiser Slimline-E V3 is designed for flush mounting into a wall-mounted back box.

A minimum back box depth of 35 mm is required.

Important Installation Requirements

• Mount the thermostat at eye level.
• Do not position it near a direct heat source.
• Keep the thermostat away from conditions that interfere with accurate air temperature sensing.
• Do not cover the thermostat with curtains or obstruct it with furniture.
• Avoid placing it close to electrical fires, televisions, or lamps that could affect temperature readings.
• Do not apply excessive pressure to the LCD screen, as this may permanently damage it.

Step 1: Remove the Front Panel

1. Locate the slots on the bottom edge of the thermostat.
2. Insert a small flat-head terminal screwdriver into the slots.
3. Carefully separate the front section from the back plate.
4. Place the front section somewhere safe while the back plate is installed.

Step 2: Connect the Thermostat Wiring

The thermostat wiring must follow the Slimline-E wiring diagram supplied with the manual.

The diagram identifies connections for the 230V AC mains supply, heating load, floor temperature probe, and optional remote air probe.

Electrical connections must follow the manufacturer’s illustrated terminal arrangement.

Step 3: Secure the Back Plate

1. Position the thermostat back plate against the wall back box.
2. Align the mounting holes.
3. Screw the back plate securely into the back box.

Step 4: Reattach the Thermostat

1. Position the front panel against the installed back plate.
2. Carefully clip the front panel into place.
3. Check that the front section is properly attached.

The physical installation procedure is illustrated in the original PDF on page 7.

Selecting the Operating Mode and Factory Reset

The Slimline-E V3 supports two primary operating modes.

Programmable Thermostat Mode is the default operating mode.

Mode selection is performed through a procedure that also factory-resets the thermostat.

How to Change the Operating Mode

1. Press and hold the Power button until the display turns off.
2. Press and hold the Power and Up buttons together.
3. Continue holding until the LCD turns on.
4. All screen icons will appear briefly.
5. The thermostat will perform a factory reset and display the mode selection options.
6. Use the Up or Down button to select the required mode.
7. Select 01 for programmable thermostat operation or 02 for time clock operation.
8. Press A to confirm the selection.
9. Press Power to turn the display on.

Factory Reset Procedure

The factory reset is performed using the same button sequence.

Pressing and holding Power + Up while the display is off starts the factory reset and mode selection process.

After the reset, the required operating mode must be selected and confirmed.

Because this process performs a factory reset, it should not be treated as an ordinary setting adjustment.

Mode 01: Programmable Thermostat

In Mode 01, the Slimline-E V3 operates as a temperature-controlled heating thermostat.

It can maintain a manually selected temperature or follow programmed comfort levels throughout the day.

This is the mode used for controlling electric underfloor heating with the appropriate floor sensor configuration.

Setting the Clock in Thermostat Mode

The clock should be configured before setting a heating schedule.

How to Set the Time and Day

1. Make sure the thermostat is switched on.
2. Press the Clock button twice.
3. Use the Up and Down buttons to set the hour.
4. Press H to confirm.
5. Use Up and Down to select the minutes.
6. Press H to confirm.
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 optional Feature 11 is configured for manual, non-programmable operation, the Clock button does not respond.

Temperature Sensor Settings and Display

The Slimline-E V3 can monitor room temperature, floor temperature, or a combination of sensors.

The selected sensor arrangement determines how the thermostat monitors temperature.

Available Temperature Sensor Configurations

When an air sensor and floor sensor are used together, the floor sensor acts as a temperature-limiting sensor to help prevent floor overheating.

Important Floor Sensor Requirement

The built-in air sensor alone must not be used to control electric underfloor heating.

For electric underfloor heating, a floor sensor must be used either on its own or in combination with an air sensor.

How to View the Floor Temperature

When both air and floor sensors are selected, the LCD normally displays the room temperature.

To view the floor temperature:

1. Press and hold the A button.
2. Continue holding until FLOOR TEMP appears on the screen.
3. Read the displayed floor temperature.

The FLOOR TEMP indicator identifies the sensor reading being displayed.

Programming the Thermostat Comfort Levels

The programmable thermostat allows four comfort levels to be configured for each programmed day or day group.

The available comfort periods are:

1. WAKE
2. LEAVE
3. RETURN
4. SLEEP

Each period has an adjustable starting time and required temperature.

Available Heating Schedule Modes

The programming mode is selected using optional Feature 10.

How to Program Heating Times and Temperatures

1. Press the Clock button once.
2. The thermostat will display the day or group of days being programmed.
3. Use the Up and Down buttons to select the required WAKE time.
4. Press H to confirm.
5. Use the Up and Down buttons to select the WAKE temperature.
6. Press H to confirm.
7. The display will move to the LEAVE period.
8. Repeat the time and temperature settings for LEAVE, RETURN, and SLEEP.
9. Continue through any additional day or day-group settings required by the selected programming mode.
10. Press A to save the program and return to the main screen.

Programming by Day Type

5/2 Day Programming: The thermostat initially displays Monday through Friday. After those settings have been configured, Saturday and Sunday appear for separate weekend programming.

7 Day Programming: Each day is configured independently, beginning with Monday.

24 Hour Programming: The same four comfort levels are used for all days.

Skipping an Unused Comfort Period

A comfort period can be left unused by setting its time to the displayed –:– value.

The thermostat will then ignore that period.

Adjusting the Set Temperature

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

How to Change the Temperature

1. Press the Up or Down button.
2. The LCD will display SET and the current target temperature.
3. Use Up or Down to select the required temperature.
4. Press A to confirm and return to the main display.

How Long Does the Temperature Adjustment Last?

The effect depends on whether the thermostat is operating in programmable or manual mode.

For a temporary temperature setting that must remain active for a specific duration, the Temperature Hold feature can be used.

Temperature Hold Function

Temperature Hold temporarily overrides the current heating schedule and maintains a different temperature for a selected period.

How to Set a Temperature Hold

1. Press H to enter Temperature Hold.
2. Use the Up and Down buttons to select the required hold duration.
3. Press H to confirm the duration.
4. Use Up and Down to select the required hold temperature.
5. Press A to save the settings and return to the main display.

The LCD will show HOLD FOR and the remaining hold time.

The displayed time counts down until the hold period ends.

When the countdown finishes, the thermostat automatically returns to its normal programmed heating schedule.

How to Cancel Temperature Hold

1. Open Temperature Hold using the H button.
2. Reduce the hold duration to 00:00.
3. Complete the setting procedure.

The temporary hold is canceled.

Holiday Mode in Thermostat Operation

Holiday Mode maintains the frost protection temperature for a selected number of days.

At the end of the holiday period, the thermostat automatically returns to its programmed operation.

How to Activate Holiday Mode

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

The suitcase symbol remains visible while holiday mode is active.

When Does Holiday Mode Begin?

A holiday period begins at 00:00 on the day following its configuration.

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

• Saturday counts as the first holiday day.
• Sunday counts as the second holiday day.
• The normal programmed heating schedule resumes at 00:00 on Monday.

How to Cancel Holiday Mode

1. Open the Holiday setting using H.
2. Reduce the number of holiday days to 00.
3. Confirm the setting.

Frost Protection Mode

Frost Protection allows the thermostat to maintain a reduced temperature when normal heating is not required.

When this mode is active, heating operates only when the measured temperature falls below the selected frost protection temperature.

How to Activate Frost Protection

1. Press Power once.
2. The frost protection icon appears on the LCD.
3. The thermostat operates according to the selected frost protection temperature.

When heating is required in this mode, the flame icon appears.

How to Cancel Frost Protection

Press Power once again to leave frost protection mode.

Frost Protection Temperature Settings

The frost protection setting can be affected by the optional frost mode configuration.

When the thermostat display is switched off and frost protection is enabled, the frost symbol is used to indicate heating demand in place of the flame symbol.

Turning the Thermostat On or Off

The thermostat can be switched off using the Power button.

Turning the Display Off

1. Press and hold Power.
2. The display will turn off.

The manual describes the display and heating output as switched off, subject to the optional frost protection setting.

Turning the Thermostat On

Press Power once to switch the thermostat display back on.

Understanding the Heating Flame Icon

• Flame visible: Heating is being requested.
• Flame absent: The thermostat is active but does not currently require heating.
• Flame flashing: Optimum Start is operating.

The absence of the flame icon does not mean that the thermostat itself has been switched off.

Advanced Thermostat Settings and Optional Features

The Slimline-E V3 includes 11 optional thermostat features.

These settings control temperature display preferences, sensor selection, switching behavior, heating programs, and other functions.

Most optional settings do not require changes during normal use.

How to Access Optional Thermostat Features

1. Press and hold Power to switch the thermostat off.
2. Press and hold the Clock button until the optional settings screen appears.
3. The LCD will display a feature number and its setting value.
4. Press Clock to move through the available features.
5. Use Up and Down to change the selected value.
6. Press A to confirm the settings.
7. Press Power to switch the thermostat back on.

Optional Features Settings Table

Feature 01: Temperature Format

This setting changes the temperature display between Celsius and Fahrenheit.

The factory setting is Celsius.

Feature 02: Switching Differential

The switching differential determines how far the measured temperature can fall below the set temperature before heating switches on.

For example, when the target temperature is 20°C:

• With a 1°C differential, heating starts at 19°C and stops at 20°C.
• With a 2°C differential, heating starts at 18°C and stops at 20°C.

The default differential is 1°C.

Feature 03: Frost Protection When Display Is Off

This option determines whether frost protection remains active when the thermostat display is switched off.

The factory setting is Enabled.

Feature 04: Output Delay

Output Delay is used to prevent rapid switching of the heating output.

The setting can be adjusted from 0 to 15 minutes.

The default setting is 0 minutes, meaning that no output delay is applied.

Feature 05: Temperature Up/Down Limit

This setting limits the amount of temperature adjustment available through the Up and Down buttons.

The limit also applies when the keypad is locked, allowing restricted temperature adjustment.

The available setting range is 0–10°C, with a default of 0.

Feature 06: Sensor Selection

This setting determines which temperature sensors are used.

When both air and floor sensors are enabled, the floor sensor is used to limit the floor temperature.

The air-only setting must not be used for electric underfloor heating.

Feature 07: Floor Temperature Limit

This setting establishes the maximum floor temperature limit when the floor sensor is enabled.

The adjustable range is 20–45°C.

The factory default is 27°C.

When the floor sensor reaches the configured limit, the floor temperature limit indicator appears on the display.

Feature 08: Optimum Start

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

The thermostat calculates the heating time using the observed temperature increase rate.

This allows heating to begin as late as possible while working toward the programmed temperature.

The setting range is 0–3 hours, with 0 as the factory default.

Feature 09: Rate of Change

Rate of Change represents the number of minutes the thermostat has calculated are required to increase the building temperature by 1°C.

For example, a rate of change of 20 represents an estimated 20 minutes to raise the temperature by 1°C.

The thermostat continues monitoring heating performance and updating this calculation.

Feature 10: Programming Mode

This setting selects the heating schedule structure.

• 00: 5/2 Day Programming
• 01: 7 Day Programming
• 02: 24 Hour Programming

The factory default is 5/2 Day Programming.

Feature 11: Thermostat Mode

This option determines whether the thermostat uses a heating schedule or operates with a constant manual temperature setting.

• 00: Manual / Non-Programmable
• 01: Programmable / Comfort Levels

The factory default is Programmable.

Locking and Unlocking the Thermostat

The Slimline-E V3 includes a keypad lock to restrict normal control changes.

How to Lock the Thermostat

1. Press and hold A and Down together.
2. Continue holding for 10 seconds.
3. A lock icon will appear on the display.

The lock icon indicates that the keypad lock is active.

How to Unlock the Thermostat

1. Press and hold A and Down together for 10 seconds.
2. Continue until the lock icon disappears.

The keypad lock icon is displayed only while the lock is active.

Recalibrating the Thermostat Temperature

The Slimline-E V3 includes a temperature recalibration procedure.

How to Recalibrate the Temperature Reading

1. Press and hold Power to switch the thermostat off.
2. Press and hold Power and Down together.
3. Continue until the calibration temperature appears on the LCD.
4. Use Up and Down to select the new calibration temperature.
5. Press A to confirm.
6. Press Power once to switch the thermostat back on.

The recalibration screen displays the temperature value together with the SET indicator.

Thermostat Error Codes and Troubleshooting

The Slimline-E V3 displays an error code when certain temperature sensor faults are detected.

Error Code Reference

Error E0: Internal Sensor Fault

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

The manufacturer directs users to contact the thermostat retailer for assistance.

Error E1: Floor Sensor Fault

Error E1 is associated with the remote floor temperature probe.

The code may appear when:

• The floor probe has not been connected.
• The floor probe has been wired incorrectly.
• The floor probe is faulty.

The floor probe connection and sensor condition should be assessed by the installer or appropriate service professional.

Error E2: Remote Air Sensor Fault

Error E2 relates to the remote air temperature probe.

It can indicate:

• A missing remote air probe connection.
• Incorrect probe wiring.
• A faulty remote air probe.

The sensor connection and probe condition require checking.

Mode 02: Time Clock

The Heatmiser Slimline-E V3 can also operate as a time clock.

In this mode, the device controls an electrical output based on programmed switching times or a countdown period rather than regulating room temperature.

The manual identifies possible time clock applications such as:

• Hot water
• Towel rails
• Lighting

The connected equipment must be wired according to its manufacturer’s instructions.

Important: Time Clock Mode must not be used to control electric underfloor heating.

Time Clock LCD Display

Time Clock Mode uses a different set of display indicators from Thermostat Mode.

The TIMER ON and TIMER OFF indications are used to display the output state.

Setting the Clock in Time Clock Mode

The number of Clock button presses required depends on the selected time clock configuration.

• In Countdown Mode, press Clock once.
• In 5/2 Day, 7 Day, or 24 Hour Programming Mode, press Clock twice.

How to Set the Time and Day

1. Open the clock setting using the required number of Clock button presses.
2. Use Up and Down to set the hour.
3. Press H to confirm.
4. Use Up and Down to set the minutes.
5. Press H to confirm.
6. Use Up and Down to select the day.
7. Press A to save the settings and return to the main display.

Programming Time Clock Switching Times

The programmable time clock can control an output through four switching periods:

• WAKE
• LEAVE
• RETURN
• SLEEP

Each period can have a TIMER ON and TIMER OFF time.

How to Set Switching Times

1. Press Clock once.
2. The display will identify the current day or day group.
3. Use Up and Down to select the TIMER ON time for WAKE.
4. Press H to confirm.
5. Use Up and Down to select the TIMER OFF time for WAKE.
6. Press H to confirm.
7. Repeat the procedure for LEAVE, RETURN, and SLEEP.
8. Continue programming additional days or groups as required.
9. Press A to save the switching schedule and return to the main display.

Time Clock Programming Modes

When 5/2 Day Programming is selected, the thermostat presents the weekend settings after the weekday schedule.

Skipping an Unused Switching Period

Set the switching time to –:– to leave a period unused.

The time clock will ignore that switching period.

Countdown Timer Mode

Countdown Mode allows the output to remain active for a selected duration.

How to Start a Countdown

1. Use Up and Down to set the required countdown duration.
2. Press A to confirm.

The HOLD FOR indicator appears and shows the remaining countdown time.

The output is active while HOLD FOR is displayed during the countdown.

How to Cancel the Countdown

Reduce the countdown duration to 00:00.

Time Clock Manual Override

The time clock includes a manual override function.

This allows the current programmed timer status to be changed temporarily.

How to Override TIMER ON

When the current output status is TIMER ON:

1. Press A.
2. The output changes to TIMER OFF.
3. TIMER OFF flashes on the display to indicate an override.

The time clock automatically resumes the programmed switching schedule at the next scheduled switching time.

Holiday Mode in Time Clock Operation

Time Clock Holiday Mode keeps the timed output off for the selected holiday period.

Once the holiday duration ends, the time clock returns to the programmed switching schedule.

How to Activate Time Clock Holiday Mode

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

The suitcase icon remains visible while holiday mode is active.

Holiday Start and End Times

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

For example, a two-day holiday configured on Friday begins on Saturday and ends when normal programming resumes at 00:00 on Monday.

How to Cancel Holiday Mode

1. Open the holiday settings using H.
2. Reduce the holiday duration to 00 days.
3. Confirm the setting.

Locking the Time Clock

The keypad lock works in Time Clock Mode.

How to Activate the Lock

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

How to Remove the Lock

Repeat the same 10-second button combination.

The lock symbol disappears when the keypad is unlocked.

Advanced Time Clock Settings

The Slimline-E V3 provides two optional settings specifically for Time Clock Mode.

Available Time Clock Features

Feature 01: Programming Mode

This determines how switching times are organized.

The default setting is 5/2 Day Programming, with separate schedules for weekdays and weekends.

Feature 02: Countdown or Programmable Operation

This determines whether the time clock uses a countdown or programmed switching times.

• 00: Countdown Timer
• 01: Programmable Switching Times

Programmable operation is the factory default.

How to Change Time Clock Optional Settings

1. Press and hold Power until the time clock display switches off.
2. Press and hold Clock until the optional feature screen appears.
3. The feature number and current value appear.
4. Use Clock to move between the available features.
5. Use Up and Down to change the selected setting.
6. Press A to confirm.
7. Press Power to switch the time clock back on.

Heatmiser Slimline-E V3 Wiring Diagram

The Slimline-E V3 wiring diagram shows the electrical connections for the mains supply, heating element, floor temperature probe, and optional remote air probe.

The wiring diagram is located on PDF page 39 (manual page 38).

Wiring Terminal Identification

The diagram shows the following terminal labels:

The wiring diagram shows a 230V AC supply with an RCD arrangement.

The floor probe is connected to the sensor terminals indicated in the drawing, while the optional remote air probe has its own illustrated connection.

The heating mat or cable is shown connected to the switched LOAD output and the relevant neutral terminal.

Floor Probe Connection

The floor temperature probe is used to measure floor temperature.

When it is enabled, the thermostat can use its reading for temperature regulation or floor temperature limiting, depending on the configured sensor mode.

The correct connection arrangement is shown in the manufacturer’s wiring diagram.

Remote Air Probe Connection

The wiring diagram also illustrates an optional remote air probe.

The remote air sensor can be selected through Feature 06.

Electric Underfloor Heating Sensor Requirement

Electric underfloor heating must not be controlled using only the built-in air sensor.

The installation must use the floor sensor independently or in combination with an air sensor.

The manufacturer also prohibits using Time Clock Mode to control electric underfloor heating.

The original wiring diagram should be used as the reference for the exact electrical connections.

Frequently Asked Questions

1. How is the Heatmiser Slimline-E V3 thermostat programmed?

The Slimline-E V3 is programmed by pressing Clock once in programmable thermostat mode.

The WAKE, LEAVE, RETURN, and SLEEP periods can then be assigned individual start times and temperatures. Up and Down change values, H confirms each setting, and A saves the program. The thermostat supports 5/2 Day, 7 Day, and 24 Hour programming.

2. How is the Heatmiser Slimline-E V3 factory reset?

Switch the thermostat display off by holding Power. Then hold Power and Up together until the LCD turns on. The screen briefly displays its icons and performs a factory reset before presenting the operating mode selection. Use Up and Down to choose Mode 01 or Mode 02, press A to confirm, and press Power to turn the display on.

3. Why is the Heatmiser thermostat not calling for heat?

The flame icon indicates heating demand. When the icon is absent, the thermostat does not currently require heating to maintain its selected temperature.

The programmed comfort level, current set temperature, active frost protection, and any displayed error code can help identify the current operating state.

4. What does E1 mean on a Heatmiser Slimline-E V3 thermostat?

Error E1 indicates a problem associated with the remote floor probe. The probe may be disconnected, incorrectly wired, or faulty. The floor probe connection and sensor condition require assessment.

5. How is the Heatmiser Slimline-E V3 thermostat unlocked?

Press and hold the A and Down buttons together for 10 seconds. The keypad lock symbol disappears when the lock is removed. The same button combination activates the lock.

6. What is the default floor temperature limit on the Slimline-E V3?

The factory default floor temperature limit is 27°C. The setting can be adjusted between 20°C and 45°C through optional Feature 07 when the floor sensor is enabled.

7. Can the Slimline-E V3 control electric underfloor heating without a floor sensor?

No. Electric underfloor heating must not be controlled using the built-in air sensor alone. A floor sensor must be used either independently or together with an air temperature sensor.

8. How is the Heatmiser Slimline-E V3 switched between thermostat and time clock modes?

Turn the display off, then press and hold Power and Up until the LCD starts. After the factory reset sequence, select Mode 01 for Programmable Thermostat or Mode 02 for Time Clock. Press A to confirm and Power to turn the display on.

Customer Support and Manufacturer Information

Heatmiser provides technical support and product information through its official website and support team.

The manufacturer’s website provides further product information and technical specifications.