I have a Vokera excell 80 SP ---10 years old recently serviced(new diaphragm etc) central heating appears ok its the hot water thats the problem - it comes on and heats up but will go cool and warm up again even though the burner is continually burning during this operation:? I have swiched the heating off and it still happens. Also the same problem when using the shower (and we all know what that can be like) no changes in system and has been flushed using TSSM-4 sludger remeover etc
any ideas - yes a new system has come to mind but if there is a way round it for a few years it would be well received

jaf, December 2007

AFAIK he control system for these is pretty crude, just high flame low flame or off. it isn't proportional. If you find a solution please post it. Are you sure the main burner is realy still buring, not just the pilot?)

c, December 2007

Check burner for high and low flame, the burner may modulate possibly if either fan dirty or domestic hot water heat exchanger blocked. You could change 'ntc'.

Big A, December 2007