DIY Doctor UK DIY Forums

please help, my "british gas f2" potterton boiler keeps cycleing every 30 secs or so.

central heating~ from cold the boiler will stay on fine untill the return pipe to boiler is up to temp (all rads warm) then will cut out as it should. now the problem starts as the boiler will turn on for 30secs then off for 30 secs and so on until the room stat turns the system off.

hot water~ same again boiler works fine untill the return water pipe is up to temp then the boiler cuts in and out every 30secs.

the 3 way valve seems to work fine and so does the pump, i have had 2 plumpers/boiler repaiers round and they say that it is not right but cant say why. the boiler has just been serviced as well.

any ideas? cheers paul

I am not familiar with this boiler, so can only advise in very general terms. The manufacturers instructions which should have been left with you ( if not try downloading a set from the internet) when the boiler was installed usually have flowcharts at the back for fault tracing. Make sure that any Corgi engineer has access to them. At a guess , he should be concentrating on the thermostats within the boiler that prevent overheating. Either they are not working or the boiler is overheating for reasons which must be investigated. Definately not a diy job, you need a competent professional.
Was the boiler working ok before the service.

yeah it was the same before the service.
fitted a new temp sensor stat today (goes on the outlet water pipe on the left hand side, the higher of the two) clips to the water pipe one end and is the boiler controls the other end. But its still the same. :cry:

any idea were on the net i can get the manual/ diagnostic instructions from?

cheers

I had a similar problem with a potterton boiler and changed the temp stat with no effect. Mine was getting so hot it was firing boiling water into the loft expansion tank. It turned out that there was a valve in the airing cupboard that had been turned nearly off. This valve controlled the return flow to the boiler, once turned fully on problem was solved, this might be worth a look.

For manual try Potterton There should also be a phone number to ring if the manuals are not on their web site.

Each radiator in your system should be trimmed so about 15 deg between inlet and outlet when all radiators are running. The same with your hot water there are two basic ways boilers work. One when hot enough they turn off. Two when they start to get hot water returned they start to turn down until they reach min then they turn off. The latter are used with TRV's but the former were never originally designed for TRV's and have problems if two many radiators are fitted with them. I have old system and only up-stairs radiators are fitted with TRV's
Over 85 deg causes both burns from radiators and water loss and below I think 55 deg legionnaires so out at 60 with 10 deg drop in pipe work and 15 deg on each radiator. Heating guys can normally do it by feel but I need temp gauges. Of course once any TRV's start to work it messes it all up so must be done with manual things or TRV's fully open.