DIY Doctor UK DIY Forums

Hi :)
I need to replace my old British Gas timer emp2 and seperate switchmaster thermostat with modern units that are compatible and as easy to fit as possible for a ‘non expert’ let’s say ;)

I’ve read it is possible to get replacements that clip onto the existing backplates for ease of installation??

Thanks for any thoughts and purchase links :)

Hi bigonabianchi
It may well be possible but it is beyond the scope of this forum. This is because we cannot tell what has been done with the wiring and do not know what thermostat you have.
Contact a local heating specialist who has electrical experience.
Regards S

There is a reasonably standard back plate, but if you take Hive as an example, the single and duel versions have the wires in different places on those plates.

So step one with DIY is find out what you have. Some times you can find the wiring diagram with google, some times it is written on the device.

The very old thermostat had a mercury file and they had to be kept level, but latter the contacts clicked across so there was a different on and off temperature, to get them closer together they had a resistor which heated up, but it was not always connected, this cause a high hysteresis, however with some systems this is not a bad thing.

So roughly boilers are two types, the on/off type and the modulating type, both system and combi can be either type, the old on/off any old thermostat will do, but with the modulating type (flame height alters) the wrong thermostat can cost you money. And may seem odd but often the more expensive are not suitable but cheap are.

Some thermostats use what is called an mark/space ratio to stop the temperature over shooting, they start switching the boiler off/on as it approaches the target temperature, however this will completely mess up the controls on a modulating boiler, there are two ways the modulating boiler can work, a thermostat connected to the ebus, or temperature of the return water.

So you say want to keep it simple, so first question is have you got thermostatic radiator valves (TRV)? If so then easy way is to replace the heads, you can get very cleaver heads that talk to the wall thermostat connect to internet and do all sorts of very cleaver stuff, but there are also simple stand alone units, the eQ-3 is a good example.

So with the eQ-3 (The terrier i30 is very similar) you have a display in degrees C not a silly *123456 so you actually know what the setting is, and you can program a schedule into the head, so every radiator has it's own control.

So before going into how to fit a new programmer and thermostat, look at the eQ-3 TRV head. Two versions with and without bluetooth price around £10 without and £15 with bluetooth, the bluetooth means you can program with a phone and you can set two to work the same when two radiators in the same room, but once programmed I find rarely use the bluetooth, it has a eco/comfort button and temperatures can be set, so when I walk into a room I press the button and it normally returns to standard on next scheduled change, or turn dial, or push dial many ways to get same result.

Anyway see what you think, and then I will expand on what you need.