BG 330 Gas Boiler Powered on but won't run, no error code

1 Jul 2007
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United Kingdom
BG 330 gas boiler was working fine then no heat/hw yesterday, I've been changing rads, few at a time and a few days back did get an F5 overheat error. Got air out and reset and all was fine. Fitted 2 more rads yesterday, bled out air, system was working fine in the morning then no heat/hw on the evening schedule.

Been through all the electrics today, boiler has permanent live and switched live demand via valves / thermostat ok but green light not coming on and boiler not running, pump also not running, pump live not coming back from boiler, small LCD on 330 displaying water temp of about 11-14 degrees. When first powering on hear a puff and whir from it but doesn't run, no red light and no error code though.

Any idea what this might be, anything simple I could have missed caused by changing rads? Believe boiler is circa 2006 but only been here a few months so don't know its history, if its not something simple caused by the rad changes unsure whether it would be worth getting fixed or just go for a new boiler given its age?
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Already checked the overheat, button wasn't out and it has continuity ok, cannot find anything obvious, PCB is powered ok, fuse ok, all I get is the water temp reading on the LCD (about 12 degrees), brief whir and puff as its powered on it, then it sits there and does nothing, no fault code and no green or red led. Any other ideas?
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Finally found the fault after tracing the demand switched live through further into the boiler, on the 230V controls interface PCB there are two 100k resistors next to the opto couplers, one was open circuit circled on the picture below, replaced it and all back to normal. I wonder how many boilers would be written off for the sake of 10p resistor. Hope this helps others, if the boiler seems powered as normal but not running check the demand signal all the way through.


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