The boiler(Vokera 80sp) fires up from cold when main power is switched on, it stops about 10 mins and cuts off and won't fire again, unless swith off main power and wait for few minutes and switch on. I found out the problem is when it cuts off , the fan is idle( it should slow run when boilt is not firing up). The slow speed resistor is ok, measured as 573 ohms. Fan is about 4 year old, runing pretty good. Flow switch is performing well. Which components are faulty to cause this problem? A faulty PCB?

Andy, February 2010

Bad solder joints are common on the resistor, the flow microswitch often goes intermittent then fails. You need to use a voltmeter to find the break in the electrical circuit, do so with care as the thing is live, and use a earth leakage breaker in the supply if at all possible. It could be the fan bearings are sticky, try some wd40 on them (not a long term solution). Actually working on the fan is meant to be a corgi job as it is inside the sealed chamber.

c, February 2010