Thermostat exchange to Timeguard Booster FBT4 (mains eco compact boiler)

8 Nov 2022
Reaction score
United Kingdom
Quick bit of advice i have a mains eco compact combi. Currently how i activate it for the heating is by turning the old thermostat to the temperature i want-not via the actual boiler which seems to be how the boiler functions. Im intending on swapping it to the Timeguard 2 hour booster as people keep forgetting to turn it off.

Does anyone have any advice on this? Is this the correct thing to do in terms of will it work? - im assuming the temperature of the heaters is from the boiler settings?

And the only other query I have is - is it relatively straight forward to do this exchange no handyman has been keen for the job and I feel its managable.


  • IMG_20221106_143846.jpg
    79.7 KB · Views: 34
  • s-l1600.jpg
    221 KB · Views: 27
Sponsored Links
I don’t why you’ve bought that? Standard single channel time clock would suffice.
Is this the correct thing to do in
No, it's entirely wrong.

With that timer instead of a thermostat, there will be no control of the room temperature.
What will happen is the boiler will switch on at maximum and stay that way until the time runs out.
Result = overheated rooms and vast quantities of gas wasted, and then the rooms cool until someone bothers to stab at the timer buttons once again. Probably the most inconvenient and inefficient use of a heating system ever known.

Realistic options:
1 - use the thermostat that's there properly. This means setting it to the room temperature required and leaving it there. Constant adjustment is not required, it will turn the boiler on and off as the room temperature varies.
It's also set to 30C in the picture, which is ridiculously hot. Try 20.

2 - If it's necessary to have different termperatures at different times, such as cooler at night, then replace it with a programmable thermostat. That can be set to have different temperatures for different times of the day.
As with the existing thermostat, it's set it once and leave it that way.

3 - If you want the same temperature when the heating is used and also times where no heating is used at all, it can be done with the existing thermostat and a separate timer. However the programmable thermostat can also do that, so buying a separate timer doesn't make much sense.

4 - For people who go out of the house leaving it unoccupied and are incapable of setting a timer, devices such as the Nest / Hive / Tado will control the heating for you by detecting when your smartphone is not in the building.
Only of use where everyone has a smartphone and also has the app installed. Otherwise it's just a very expensive programmable thermostat.

im assuming the temperature of the heaters is from the boiler settings?
The boiler settings are for the maximum temperature of the water circulated through the radiators. That is unrelated to the temperature of the rooms.
It's also another thing that should be set once to something like 55C when the boiler is installed and never changed.
  • Thanks
Reactions: CBW
From what you say, I understand that you only have just the manual dial thermostat to select the room temperature required and that there is no timeswitch on the boiler or elsewhere.

The Main Eco Combi has been around a long time, so there are a few versions and some (but not all) have built in time control. If you do have a timer like the example below, the movable sliders allow you to select the time that you want the heating to be on and off.


If yours doesn't have a timer built in, you could just swap the old thermostat for a programmable thermostat, that will allow you to set a comfortable room temperature you want to maintain, and choose the times that you want the heating to be on.

im assuming the temperature of the heaters is from the boiler settings?
By "the boiler settings", I assume that you are referring to the boiler thermostat. Then yes it only regulates the radiator temperature. It does not control the room temperature the room thermostat does that.
Last edited:
  • Like
Reactions: CBW
Sponsored Links
Most programmable thermostats have 4 to 6 slots a day, some have many more, so setting times is the normally method, I had one which would set to 16ºC six times a day, so you had to return to it to switch it up, however in the main boilers control many rooms, so using programmable TRV heads works better.

My heads have a Eco, Comfort, and boost setting. Plus a wheel where you can dial the temperature, 61dmtMm13BL.jpg they cost me £15 each in 2019, and again like the wall thermostat can be programmed to a low back ground heat, many times a day, so easy to set so unused rooms are not heated.

Boilers will auto shut down when hot water returns, but they will cycle on/off every so often, so using a thermostat as well can stop the cycling, but unlike the old heads TRV.jpgwhere once set to 6 it stays at 6, the electronic head will return to programmed setting at times selected.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local