Hi, I am looking to fit a Thermostat to a Worcester Bosch 24i Combi boiler, and have 3 questions.

1. How do I know which makes/models are compatible?

2. Which room is best, I have TRV's on each rad, only place without is hall by front door which is the coldest room, is it OK to put a stat in a room with TRV's?

3. Will it run in conjunction with the existing mechanical timer, (ie will the boiler come on at the times set by the timer apart from when the temp is already above the set stat temp), or is it best to get a programmable one to set new times and disconnect the mechanical one?

I am asking as I don't want to guess and buy the incorrect one.

Thanks in advance for any replies.

Rich.

I am not familiar with your system and if I was sure somebody else here was, I wouldn't answer. Does your system use the common 24 volt transformer voltage for the controls? If so, you have a wide variety of thermostats that will work. If not, you are restricted to thermostats designed to use the voltage your system uses, or you will have to use a relay.

Again, I don't know what a TVR is. The thermostat needs to be away from cold walls, drafts, sources of heat, etc. so it can accurately measure the room temperature.

If you leave your mechanical timer connected, the boiler will run when either it or the new thermostat, or both call for heat. The thermostat will not allow the timer to cut back the heat at night. If that is what you want, you may need to switch to a programmable thermostat.

Thanks for replying Labman, it looks from the boiler diagram that it requires 3x230V connections, neutral, live and a switched live, the same as the mechanical programmer by the looks of it.

By TRV I mean the thermostatic radiator valves on each radiator, I do have these but they are not brilliant, some stay on, which I will replace the heads of soon so it would be nice to have an overriding control in our lounge.

I was looking through the Screwfix catalogue, there seemed to be loads, but I then realised some were timeswitches and not thermostats.

Regarding keeping the mechanical programmer connected, if the boiler fires when any one of them calls for heat, the mechanical programmer then calls for heat when the thermostat says the correct temp is already reached, will the boiler stay on or will the thermostat some how override the mech programmer?

Cheers,

Rich.

Sorry but I'm going to say this is a good one for the pro's to answer. I have seen to many different ways installers, control and wire these things. They should give you a price before they do anything and you can learn a lot by asking them a few questions, just give the poor guy a few minutes to get the system figured out in his head before you start with the questions.