What you said above, i assume it works however most times when hot tap open full, is that correct?
if so id be looking towards the low gas pressure setting.
ch fires on high then drops to low which is when it could be going out.
dhw open full would prob keep burner on high keeping burner fired.
dhw open partially, burner would have to modulate down to low and could be going out then.
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if it was faulting in the same way on both all the time id be thinking of a primary thermistor but seems more gas valve related to me.
maybe time for an engineer call as a quick 2 min check would confirm/rule out pressure problem
iain
September 2008