I had a plumber round today who didn't have clue and started talking rubbish that the hot water must heat first, then the heating will work.
My systen works as most, I can either choose to have heating/hotwater or both.
I can heat the water no problem
When the water is on, i can choose to have heating as well and the rads start warming up (slowly)
If i decide i just want heating, I click the thermostat round, I can hear the valves opening in the airing cupboard. The boiler starts to light, then stops.
It seems to me that the boiler is working and that there is some sort of communication problem between the programmer and or thermostat to the boiler, but really i have no idea and am open to any suggestions
I don't know which boiler you have but mine had the same problem and we found that BG had not done the electrics properly when installed so you need an electrician who knows about boilers etc. not a plumber. Plumbing firms usually have a pet one on call.
We were told that it is best to use the boiler at full power because it is more efficient, but in doing so we suffered the same problem as you. When the water was hot the thermostat
turned off the rads as well!
BG had the cheek to tell us we could not qualify for their warranty cover because the electrics were wrong!
A knowledgeable electrician should be your answer - good luck.
I checked the pump and the opening of the valves. Both work fine.
I started fidling with the thermostat, flicking it on and off. When i turned it on, it normally did nothing. if i flicked it a few times and therefore kept sending the signal, it turned on. I could have it on idefinately last night without an issue. Then I would try it later, turning on once...nothing. If i flicked it on and off I could get it to work.
It seems electrical to me rather than a plumbing problem, not sure thermostat or programmer.