Combi boiler not responding to TRV changes

[WabbitPoo]

We have a worcester Bosch combi. As part of me trying to decide on whether to upgrade TRVs or get a new thermostat installed, I have but the boiler onto constant heating, then switched off all rads and towel rails.

I would have excpected the boiler to (eventually) stop trying to heat the CH as its not needed. But it is still heating away, some 30 minutes later. How does a boiler decide whether to heat the CH - is it the temperature difference between flow out and return back? If so, would it suggest that I am losing heat somewhere on the pipe run (eg under a floor, or in a wall)?

Is it possible to "tune" the boiler to expect a different temperature change so I can tune it to my requirements?

 

[Steelmasons]

Room stat will switch boiler on when a call for heat (programmer on constant)..
TRV's alone will cause the burner to cycle on/off unless boiler is interlocked with room stat.

 

[WabbitPoo]

we dont have a room stat, and all rads have TRVs. If TRVs and the boiler are working as intended, should the boiler only be heating CH water when one or more TRVs are "open"?

 

[Gasguru]

You need to remove a TRV from the hall or a central zone and fix that radiator with 2 lockshield valves. In that zone install a room thermostat. Adjust that radiator so it's the last zone to come up to temperature. That way the stat should turn off the boiler when the house is up to temp. Make sure the system is balanced. There are only a few boilers whereby all radiators can be TRV'd and Worcesters aren't included.

 

[WabbitPoo]

Thanks. So, Worcesters WONT respond to all rads NOT demanding hot CH water, to be clear ? Thanks

 

[Gasguru]

Most boilers would respond by modulating the burner down to minimum and then cycling the burner on and off...wasting energy when the TRVs are shut. This is assuming they have a bypass valve fitted internally. AFAIR on the Worcester Greenstar CDi range there is no bypass (it has a modulating pump) and you must never TRV all the rads. Either way the setup you have is wrong and has been bad practice for 40 years. As I said there are only 1 or 2 boiler models ever made whereby you can TRV the whole system.