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potterton puma 100e boiler not firing. flow switch appears to be working cos can see it moving and its pushing switch on. has been making hissing noise when you put hot tap on for few secs then ok (since it was "serviced " nearly 2 yrs ago.) ive been told diverter valve buggered. or the fault finder indicates it may be air pressure valve, any ideas???? steve.

The boiler is not firing on central heating or hot water ? if it was just the diverter at fault the boiler would fire up but only for a short while.

does the pump and fan run ?

if the fan runs, does this operate the air pressure switch ?

Need more info to be able to help.

thanks for reply. boiler not firing on water or heat. pump runs when swithed on but fan not running, im assuming you mean extractor fan at top of boiler

not sure what to listen for (air pressure switch) is this located near top of boiler, quite flat with 2 pipes to it?

boiler not firing on heat or water. pump runs when heat switched on, fan not running, im assuming you mean the extractor fan located at top of boiler, air pressure switch near top on side cant hear anything.

water pressure fine, tested wires to fan and no power to it when heat switched on and pump runs

No power to fan ?
possibly PCB at fault