Hi. I have a Potterton Ultra DV40 boiler and also a Megaflo unvented water heater. When the boiler is heating the Megaflo, the burner goes and and off as the Megaflo zone valve opens and closes. However, the water in the boiler continues pumping internally in the boiler. I understand this is due to an override valve that keeps the water pubping around for a couple of minutes to reduce heat. However, the issue is that this never goes off. I have to turn all the electrics off at the master switch to stop the pump. If I switch the electrics back on, the water starts pumping around the boiler again (but at least the burner stays off and only comes on if I open the Megaflo valve).

Conversely, if I turn the boiler on to heat the CH system, the burner itself actually stays on after the the CH control tells the system to switch off. The only way to stop the burner in this case is to turn the thermostat on the boiler down to zero. If I switch all the electrics off to stop the boiler completely and then switch back on again, the burner starts up again when it shouldn't.

So in summary, turning the boiler on at the master switch always results in the pump starting up. If the boiler was previosly heating the CH loop, the burner also comes on.

Any ideas anyone ? If anyone points me to the problem they'll get be a big thankyou as my gas engineering company don't seem to know what their doing.

Many thanks, Phil.

Phil Dee, June 2007

I have an Ideal Mexico HE18 floor standing CH boiler but when the timer goes to an off period the boiler continues to burn along with the pump running.
The control panel shows a 'C' and the burner light flashes. Pressing reset does not turn it off - the only
way to turn the boiler off is to cut the mains power to it. It is only 18 months old with the new digital timer.
Any ideas?

Clive Humphrey, March 2010

i agree with the overrun thermostat being faulty and if it worked alright originally then it is probably faulty and will run alright when the new one is correctey installed ...i.e. stand at the installers side and watch what he disconnects and reconnects ..is done correctly..

mark, March 2008

Potterton boilers are suject to this fault The overun valve thermostat is faulty and needs replaceing... However check that it is correctly fitted first as this has been another major mistake by installers( It can work loose over time )

BRT, July 2007