I have a Vokera 80E condensing boiler. When heating water (not radiators), the water initially heats up ok, the goes cold for a few seconds before heating up again. This cycle continues constantlt - why? Is the gas supposed to modulate between a high and a low flame? Could there be a problem with the heat exchanger?

Martin Anderson, April 2008

Someone is asking how old the boiler is - it definately is a condensing boiler and it is 13yrs old. How does the 'condensing' section operate? Could this be part of my 'cycling hot and cold' problem?
Thanks
Martin

Martin Anderson, April 2008

Oops, I see it is an 80E, the excell 80E is not condensing, how old is the boiler?.

c, April 2008

Google 'vokera flue venturi'. Classic symptoms of dirt on the venturi pipes in the flue causing differential air pressure switch drop out. Easy job, safety legislation says it has to be done by corgi man. If you are handy with multimeter you can prove it by checking the voltage across the APS terminals when the fault appears (careful, mains voltage).

c, April 2008

hi martin, it could well be the heat exchanger causing this problem!! the flame shouldn't modulate, the working pressure for a domestic house system should be 21MLB, give or take 2 mlb which basiclally means the flame should stay constant. a suggestion is to call the gas board on 0800 111 999 and say that you have pressure problems. they should send someone out within the hour. i have been called out to a couple of jobs just like this one and its been the regulator on the inlet to the meter that has been faulty. the correct pressure in a house is 21millibar (+/- 2mlb) coming out of the regulator. however, if the pressure is too low the flame will sit low on the burner.

hope this helps

Stu, April 2008