Simple? That's what I thought then it got too cold so I called in an "expert(?)" but You also seem to think that you are also an expert - Tony
I am not an expert in as much as a heating engineer but I am also not stupid either.
I had another so called "heating engineer" look at my system yesterday and again he said that there was nothing wrong that her could see. Ok! But without shouting me down or telling me to xxxxoff please answer this......
This is a fully pumped system with 2 x electric valves. As I understand it each of these valves when opened has a feed to the pump to circulate the water in the 2 systems?
When the water in the tank is at the correct temperature the tank stat closes the HW valve and the pump should stop (providing the CH valve is not open) and likewise, if the CH is at correct temperature that valve should close and the pump should stop (providing the HW is also at the correct temperature).
Now, please bear with me on this, if the CH valve is faulty in as much as there is no feed to the pump when OPEN - and - the HW is at the correct temperature thus closing the HW valve and (theoretically) switching off the pump feed there will be no water flowing in the CH system because the pump will be off.
The boiler, on the other hand, is OFF because the temperature of the water INSIDE it (remember no pump running therefore no circulation) is at the boiler stat setting. As the water in the boiler cools slightly the boiler stat will ignite the burners and heat the boiler water again - 3 mins??? - and then switch off.
If you can follow this - is it possible that a faulty CH valve pump feed could cause this "no heating" problem after the system has been running for a couple of hours and no HW is being used like during the evening (this is when it happens) when watching TV or when we are out etc?
Taking a chance I know but if this is going to be fixed I feel the only way is to become a dammed expert or have my theory confirmed or thrown out by one.
I know the system is about 20 years old except for the new controller, pump and boiler but could my theory cause this weird occurance?
System seems normal now - wife cooking dinner and washing up etc. I know it will play up about 21:00 when the HW isn't being used.
Steve