My boiler, a Potterton Puma 80e, works fine on the hot water cycle, but randomly operates the central heating.
The heating packed up for a few days last week then one evening when I got home, all the radiators were hot and the heating was operating normally. this continued for a few more days then guess what? The heating was off one cold morning, but the water works fine.
Today, it seems, if I let the hot water run for a while, say filling a bath, the heating switches in once the tap is turned off.
No taps are dripping, the thermostat seems to be operating normally.
What could be wrong?

Phil Roberts, March 2007

it won't be your pump ....etc

Thanks. My first thought was the diverter valve, but have also fiddled with the thermostat.
Today is a warmer day and we have heating! Yet, when it goes cold it prefers to stay off.

How much does a new diverter valve cost, including fitting? A friend of mine seemed to think that someone with a bit of plumbing experience could do the job themselves - is this true?

Phil, March 2007

it won't be your pump or you wouldn't have hot water or heating. and your boiler would activate the over heat stat. something is not sending a signal for heating to come on. may be your diverter valve sticking or your stat faulty.

hi-spec plumbing, March 2007

I would suspect the circulating pump. When it appears not to work then a tap (no more!!!) on the casing of the pump with a hammer may well jolt it inot life. On the front of the pump there is often an hexagonal bolt head - a gentle turn each way on this will often free it. Hard water scale is the usual culprit.

Ray Peate
March 2007


Thanks Ray.
The pump appears to run after the hot water tap has been closed.

Phil, March 2007

I would suspect the circulating pump. When it appears not to work then a tap (no more!!!) on the casing of the pump with a hammer may well jolt it inot life. On the front of the pump there is often an hexagonal bolt head - a gentle turn each way on this will often free it. Hard water scale is the usual culprit.

Ray Peate, March 2007