I have a Myson Apollo 30/50 boiler, fitted with a manual programme ring. The programmer has the choice of Timed/Off/Continuous, HW/HW+CH and Low/O/High thermostat. The system is vented (there is an expansion/feed tank in the loft) and configured as a Y plan. The pump is a Grundfos 16/50, the three port valve is controlled by a Honeywell head and I believe the room thermostat is a bi-metallic strip type. The house has four bedrooms, and contains 10 radiators.
The system worked fine last winter and has also been happily providing ‘HW only’ all summer. However, as soon as the days started to become cooler and we switched the boiler to HW+CH, the following problem has arisen:
The boiler will come on and the system will heat up for about 15-20 minutes after which the main power circuit breaker will trip and we loose electricity to the whole house. Restarting the boiler on either HW or HW+CH will cause the power to cut out again very shortly (sometimes almost instantly sometimes a few minutes). The system does however appear to be able to provide ‘HW only’ when started from cold in the mornings.
Initially we suspected the pump, so I re-wired the pump direct to a plug and ran it from a wall socket for a few hours with no problem. Then we thought that maybe the boiler was overheating, but after a few days of no CH the boiler stopped lighting the main burner when the timer came on – the pump would still run though, and the power would trip after 20min when set to CH+HW, even though the boiler was only being warmed by the pilot.
At this point we called in an engineer. His opinion was that the boiler was ok and that given a service would last a few more years yet. He managed to get the main burner to light without changing any parts (I think he held the gas valve in whilst he flicked the boiler on?) He then tested the reactions of the 3 port valve to various boiler/thermostat settings and was happy. He suggested that the pump may be overheating, damaging its coils and tripping the power (the pump did get hot quite quickly, although no hotter than the surrounding pipework). He replaced the pump (with a Grundfos 15/50) however this has not solved the problem and the power still tripped when trying to heat the CH.
The power trips seem to occur regardless of whether the room thermostat is set so as to be On/Off, the programmer is set to Timed/Continuous or the boiler thermostat is set to Low/High (although I have not yet seen it trip with the thermostat set to 0).
Apologies for the mini essay, but any ideas that I can suggest to the engineer to help solve the problem quickly would be greatly appreciated.
The system worked fine last winter and has also been happily providing ‘HW only’ all summer. However, as soon as the days started to become cooler and we switched the boiler to HW+CH, the following problem has arisen:
The boiler will come on and the system will heat up for about 15-20 minutes after which the main power circuit breaker will trip and we loose electricity to the whole house. Restarting the boiler on either HW or HW+CH will cause the power to cut out again very shortly (sometimes almost instantly sometimes a few minutes). The system does however appear to be able to provide ‘HW only’ when started from cold in the mornings.
Initially we suspected the pump, so I re-wired the pump direct to a plug and ran it from a wall socket for a few hours with no problem. Then we thought that maybe the boiler was overheating, but after a few days of no CH the boiler stopped lighting the main burner when the timer came on – the pump would still run though, and the power would trip after 20min when set to CH+HW, even though the boiler was only being warmed by the pilot.
At this point we called in an engineer. His opinion was that the boiler was ok and that given a service would last a few more years yet. He managed to get the main burner to light without changing any parts (I think he held the gas valve in whilst he flicked the boiler on?) He then tested the reactions of the 3 port valve to various boiler/thermostat settings and was happy. He suggested that the pump may be overheating, damaging its coils and tripping the power (the pump did get hot quite quickly, although no hotter than the surrounding pipework). He replaced the pump (with a Grundfos 15/50) however this has not solved the problem and the power still tripped when trying to heat the CH.
The power trips seem to occur regardless of whether the room thermostat is set so as to be On/Off, the programmer is set to Timed/Continuous or the boiler thermostat is set to Low/High (although I have not yet seen it trip with the thermostat set to 0).
Apologies for the mini essay, but any ideas that I can suggest to the engineer to help solve the problem quickly would be greatly appreciated.