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Potterton Suprima 70 - not sure if heating system working correctly?

Postby AF1982 » Sat Dec 27, 2014 5:38 pm


I recently bought a flat and am trying to work out whether the heating system is working properly (it is working, but I am not sure whether it is doing what it is supposed to!).

I have a Potterton Suprima 70 which has had a replacement PCB at some stage. The heating is a sealed, pressurised system with 9 radiators and a mixture of standard and microbore pipes. The flat is all on one level. All but one radiator has a TRV and there is a wireless thermostat in the hall with the 'master' temperature. The boiler is in a cupboard next to the airing cupboard and hot water tank.

The system had its annual service in the summer with no reported issues, and I have both hot water and central heating. However, when on, the boiler cycles on and off repeatedly until the flat reaches the 'master' temperature. For example, when it first came on this evening it ran for 10 minutes then went off for 2 minutes, and since then has been coming on for about one minute then off for 2 minutes, then back on for one minute and off for two, and so on, for the last hour. During this time the temperature in the flat has risen from 13.8 degrees to 15.6 degrees. I am aiming for 17 degrees.

While 'off' the pump continues to run and the boiler light is flashing green, which I believe means that heat is being called for.

Should the boiler constantly be turning on and off like this, or should it fire for a longer period while the flat is heating up?

Any thoughts welcome, thank you!
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Simply Build It

Postby plumbbob » Sun Dec 28, 2014 11:20 pm

This "cycling" of a central heating boiler is perfectly normal. In fact, it is essential. If the boiler fired continuously, the water in the radiators would eventually begin to boil.

The room or "master" thermostat only monitors the air temperature in the living space. A second thermostat built in to the boiler monitors the water temperature keeping it between 60 and 80 degrees or thereabouts.
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