I have a fault with the hot water,the lights run up all the way to full heat then come down slightly when they get to about 50 degrees the hot water goes warm and the red light starts flashing on 50 deegres.The boiler is on and off constantly when this happens.

phil, September 2008

the combi does the same on c/h as just water.Going by fault finding book all pointed to fan or flue but air pressure switch found to be faulty.Also when ignition kicks in when tap turned on pressure moves down by half bar.

phil, September 2008

i would definately agree with matt on the question does it do the same on central heating?????

50 deg is fault on fan or flue which shouldnt be affected by overheat problem unless its warping venturi causing boiler to die for a small while, which happens on some eco's due to no pump over-run but ???????

my personal first checks would be, does it do the same on ch as dhw?

no, just dhw--- poor transfer from plate exchanger. id check that

yes ch and dhw---id check pump

both above pointing towards sh*tty system condition or plain part fault

hard to say when its not in front of you though, could be bonkers pcb fault.

iain, September 2008

I assume it is a combi boiler?
Have you tested your c/h to check it that works all ok?
What is your flow rate like from the hot taps?
Is there any banging and crashing from the boiler?

I assume it is a sealed system - what is the pressure i.e 1bar - does this rise quickly when using the hot water?

matt, September 2008