Potterton Performa 30 HE Central coming on during the night whent boiler set to off.

11 Apr 2009
Reaction score
United Kingdom
Hi, My Potterton Performa 30 HE has decided it wants to come on at 4 in the morning when the timer and thermostat are both set to off. When I checked the boiler the burner light is on and motor for the pump is spinning. The rear actuator on the diveter valve is out making the rear micro switch closed. Nothing on the front panel indicates that the central heating has been given the signal to run. The only way to switch the bolier off is to tuner it off.

If I set the boiler to hot water only then the heating doesn't come on, only when in the CH/HW location. The micro switches on the diverter valve have been changed. The thermostat seems to operate as designed and the timer is not giving any signals to allow the CH to engage.

I'm starting to think that it is a fault with PCB but this was only changed 1 year ago, that said it can still fail.

Any ideas?
Sponsored Links
Further updates: I think I need to be more accurate with the symptoms. I'm starting to think that the fault is related to the HW side of the system but need to recreate the original fault before I can confirm it. Rather than the central heating coming 'on' I'm starting to think the heat transfer is through the diverter based on conduction. This is the result of the burner and circulation pump sticking on after the hot water being turned off. The long term effect of the pump and burner staying on is the gradual heat up of the central heating system. next time the fault occurs I will check the position of the diverter diaphragms to check if any are sticking.
pin sticking out on divertor after hot water demand or faulty microswitch on it
Cheers for the response.

Both microswitches have been replaced with new. Tested old ones for continuity and they reacted fine. So far I have not noticed any of the diverter pins sticking out after hot water use or when testing central heating activation.

Its a strange one, the burner seems to fire up after long periods of the boiler not being used for any service. I have been woken the last two mornings with burner on. Not full demand. None of the indicators light up to say if the HW or CH has been triggered. Just the burner and pump running with rear diverter diaphragm pin in the operated (sticking out) position.
Sponsored Links
Your boiler has integral frost protection controlled by the flow thermistor (I think) when it goes out of calibration it thinks its <5c in your kitchen and brings on the burner, might be your problem.
Where abouts is the integral frost protection thermistor located? I can find any reference to this in the installation service manual. They're individual temp sensors for CH / HW and over heat thermistor. Are either of the temp sensors used for frost protection?

Thanks again Paul.
I would have guessed at the ch temp sensor but i dont know for certain.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links