Potterton Performa 28i Central Heating cutting out

[GW]

Hi all,
When I switch on the central heating on this gas combi boiler, it supplies good heat to all of the radiators in the house. Each radiator is fitted with a thermostatic valve. After about 1 hour or so, the central heating operation neon extingushes and the heat flow to the rads stops completely and the rads cool down. I have tried increasing the thermostatic valves to the maximum on selected radiators, operating the reset function on the boiler, and ensured that the problem is not down to a timer (I have switched off the timer control and made the heating fully on.), but all to no avail. The direct water heating is not affected. Hot water is supplied to the taps on demand and the boiler ignites as required. I have also noticed that the boiler fan remains on for a long time, even when there has been no demand for heating/hot water for some time. For example, I checked at 4am, which is at least 5hrs after any demand for hot water or heating and the boiler was still 'humming' which I presume is the fan. Does anyone have any idea what this annoying problem could be?

 

[gazthepottertonengineer]

humming noise is probably the pump which is quite normal !!

are any faut lights showing on boiler

 

[GW]

Usually a fault is indicated by a flashing neon. In this case none are flashing. It is just that the CH light goes of after a while. I did an experiment where I switched off the boiler for a while, switched on the CH and it came on. Then I open a hot water tap and the boiler the diverted to the hot water supply. Long after I had closed the hot water tap, the CH did not kick back into action. This seems to be the problem.

 

[gazthepottertonengineer]

its normal for it to take upto 5 mins as this is the anti cycle on the boiler working but if its much more than that then its more than likely to be pcb try replacing the temperature thermistor first though just to rule it out as its cheap and very easy to replace as its in a dry pocket

 

[GW]

its normal for it to take upto 5 mins as this is the anti cycle on the boiler working but if its much more than that then its more than likely to be pcb try replacing the temperature thermistor first though just to rule it out as its cheap and very easy to replace as its in a dry pocket

This is exactly what the problem was. This switching problem only occured when the boiler was in pre-heat mode. Two thermisors were replaced, which required a small amount of draining-off water from the boiler as one of the thermisors was on a pipe containing water.

 

[gazthepottertonengineer]

No Applause necessary