Install with ease

The BT21 thermostat is designed to make installation simple and worry free

What's in the box

Everything you need for a hassle free installation is included. 1 x Thermosphere Bluetooth programmable thermostat (BT21), 2 x fixing screws, 1 x 3m floor temperature sensor probe and installation instructions.

How to install

From wiring up the BT21 Bluetooth programmable thermostat to setting up your heating schedule, we have got you covered!

Twist & go

The patented feature enables you to install the fascia with ease and no tools are needed! Just push the dial in and twist clockwise to lock the fascia plates. It really is as simple as that!

Quick start guide

Get your thermostat and app connected in minutes. Learn what is on the thermostat, the user interface and how to set up a heating schedule.

Detailed setup guide

Learn about all the features and functionality of the thermostat and app. Discover what‘s on the thermostat, the interface and how to set up your heating schedule effectively.

Our 3 top installation tips

Twist to unlock the fascia

The patented twist and go action makes removing the fascia easy. Simply push the dial in and twist anti-clockwise to unlock the fascia plates.

Install two floor sensors

If something goes wrong you have a back up and the thermostat will always know the temperature of the floor and maintain efficiency.

Remember the preset

Save your heating schedule and all settings as a preset. Then simply copy it to all of your other BT21 thermostats in your home.

No such thing as a silly question

This could be caused by either the brightness setting or the power supply.


Brightness setting

Is the thermostat showing in the app? Yes means it has power but the display is not visible. Turn the dial to activate the display. Set brightness to 100% in the app. Send us a technical report from the app to check settings have been changed.


Power supply

  • Check that the thermostat is connected to a 230V power supply and that the power supply is switched on.
  • Check the MCB at the consumer unit is suitably rated (high enough Amps) and is switched on.
  • Check that the fuse in the spur is suitably rated (high enough Amps) and in working order.
  • Check that the fused spur for the EUFH circuit is switched on.
  • Use an electrical meter to check that there are 230V going into the thermostat. Only do this at your own risk and if you are confident and have done it before!
  • If you are not sure how to do any of this please consult a professional electrician.

Fear not! There are 3 things to check.



Check that your phone is not on flight mode and that Bluetooth is switched on.



Make sure that you are standing next to your thermostat. You can‘t control your thermostat with Bluetooth from outside your home.


Location services

Check that you have location services enabled for the BT21 app. We don‘t track you, but Android needs location services on to use Bluetooth.

If you receive an 'Error 1', you there could be 3 different reasons for this:

Sensor not connected

Check that a sensor probe is connected to the correct terminals in the back of the thermostat.

Incorrect sensor installed

Use an electrical meter on the 200K Ohms setting to check the resistance of the sensor probe. It should be somewhere between 8K and 12K Ohms depending on the temperature (table on back page).

Incorrect sensor selected in app

Open the app and perform a Factory Reset. This will erase all of your heating schedules, presets and settings from this thermostat but it will also reset the sensor modes and automatically recognise whether there is a floor sensor installed. If the error persists, send us a technical report from the app and give us a call.

If you receive an 'Error 10', there is one reason for this:

Internal clock issue

This can sometimes happen if the power is interrupted for more than 3hours. Simply connect to your phone via Bluetooth to reset the clock.

If the error persists, send us a technical report from the app and give us a call.

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We close at 5pm on 24th Dec and reopen at 7.30am on 4th Jan 2022.

Orders for next day delivery will need to be placed by 4.30pm on the 23rd Dec.