When running hot tap hot water keeps going cold for a few seconds then comes back on. Watching the lights on front of panel the DHW flow light remains on all the time but the burner light goes out. I have measured the thermister and when cold the value is about 3V raising to 1.9V before the burner shuts off. The thermister then cools to about 2.3V and then the burner comes back on which then warms the thermister again until the it reaches 1.9V and shuts the burner off again. This then repeats itself. Any help would be much appreciated..

Mike Powell, March 2006

Blast I thought I'd cracked it but the fault has reappeared thanks John for your input, I will check this out.

Mike Powell, March 2006

It could be due to limescale buildup in the exchanger causing it to overheat momentery and cut out untill it's cool enough to carry on.

d john, March 2006

I have replaced the DHW thermister and now all working OK. The voltage across the good thermister starts off at 3.2V when boiler is cold to about 2.8V when it has been running hot for a while.

Mike Powell, March 2006