Vaillant Turbomax Pro 828E on and off every couple of minutes

29 Nov 2013
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Tyne and Wear
United Kingdom
Hi, I have a Vaillant Turbomax Pro 828E boiler. In twenty years it's had a new diverter valve and new gas valve fitted, the gas valve being fitted a couple of years ago. Since I've been locked down I've noticed that once it gets up to temp it switches on and off relentlessly. It's on for a couple of minutes, cuts out for a minute and then switches back on again. When the radiator heat level is turned down to half it's off for six or seven minutes then on for a minute or so and so on.

I think it might be to do with the gas valve. The bloke who changed it was in and out in a couple of minutes. He changed the valve, checked the system for leaks and sodded off. The manual says various adjustments need to be made and the two adjustment screws that are visible are flush with the valve housing and don't look like they've ever been touched.

The return pipe into the boiler is slightly less hot than the flow pipe so I don't think there's any problem with the water getting through the system. All radiator valves have been checked and are all fully open and the radiators have been bled. Hot water is perfect.

Sometimes the gas valve will open and then immediately close again. It tries to open one or two times more and eventually the gas ignites and the boiler does its cycle.

Has anybody any idea what's up please. Also from a quick read of the forum Intergas boilers seem to be the boiler of choice. I remember seeing one on display in a plumber's merchant about a year ago and thinking the insides looked high quality. If they are the best option right now how would they be set for spares ten or twenty years from now do you think?

Many thanks in advance.
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