The symptons are as follows:
The boiler tends to run for about a minute and then cut out for 30 seconds, while the pump continues running. The pump is making a horrendous noise that doesn't sound normal, which can be heard throughout the house from each of the radiators (resonance, vibration etc).
The pipes either side of the pump are boiling to touch (hotter than any normal radiator, about 80 deg C), along with the inlet pipes for most radiators and the top of each radiator, but not the bottom or outlet pipe.
Radiators are hotter upstairs than downstairs (boiler and pump are upstairs).
When the boiler cuts out is does so with a kettling sound like the water is boiling inside, the F&E pipe is scalding and the water in the tank warm (in attic).
This problem went away for a while and has come back again, when I suddenly closed a TRV (sudden increas in flow rate on pump affecting impellor?).
Is the pump working just not at 100%, therefore not moving the water around fast enough, causing the boiler to cut out due to low flow rate (expanding into F&E tank), and not being able to heat all radiators??
I tried to replace the pump but struggles to remove the gate valve from the pump. As this involved draining the system, because I removed the gate valve from the pipe work, the pump appears to sound a bit better.
I now can not get the pilot to stay alight!!!!
It is a Thorn Apollo. The pilot not staying alight has only happened since I took the pump out and drained the system earlier today. Pilot hasn't gone out once during all my troubles with the boiler cutting out.
I really am grateful for the advice provided, thank you.
The Apollo does have an overheat stat, if you drained the boiler - when you filled it, air may have became trapped in the heat-ex. If this happened then the overheat stat would cut the pilot out.
Check the thermocouple does it have an interrupter ? electrical leads connected to the 2 spades.
If it's an apollo fanfare - do not under any circumstances remove the combustion chamber cover unless you are 100% sure how to put it back on. As they have a positive pressure case - a family was killed in my area a few year back, where an Apollo Fanfare case was not fitted properly.
If you cant get it to light - it's probably best to get a heating engineer in to repair, temporarily bridging the overheat stat with a screwdriver or similar sometimes gets the pilot going.
The overheat stat will cut the pilot out if the boiler overheats, with you draining the boiler i'm guessing that is what happened, when you turned the boiler on after re-filling there may have been sir stuck in the boiler or pump - if the boiler didn't get rid of the heat quick enough - it would cut the pilot out. It could still be the overheat stat keeping the pilot from re-lighting.
But could also just be a dirty pilot or thermocouple needs replacing.
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