Puzzled by a breakdown- Alpha CD35C

[dan_the_plumber]

Hello all.

i was called out to an Alpha CD35C. Boiler was completely dead when I arrived. The job sheet said 'boiler not resetting'

The 2 Amp fast blow fuse had gone, I replaced the fuse. The boiler ran however the PCB was actually smoking! I made some other checks and observations then phoned Alpha tech help.

The Alpha guy was very helpful. We unplugged all of the current carrying plugs from the PCB and tested that there was the correct voltage coming onto the board from the transformer at X11 or x12 was 27V which was deemed to be acceptable.

I replaced the board and the boiler fired up. It ran at about half power I think. I therefore followed the instruction to set the new PCB up and August the gas valve accordingly.

During this process I had cause to turn gas off to connect manometer. The boiler went to flame failure lockout. Light 'B' was illuminated RED constantly.

Anyway after this I tried to reset the boiler but I just would not reset. I tried switching it on and off. The boiler would just not reset!

I tested for continuity across the overheat stat that was fine.

I spoke to Alpha again. That guy told me that if the pump is not running (it wasn't) then the board must be at fault. I'd only just put a new one on though and it had been working 10 mins earlier. At this point I gave up.

I was pretty fed up to have to admit defeat and am still racking my brain as to what the problem might be.

I would be greatful for any help anyone might be able to offer!

Dan 🙂

 

[stokecity]

Is there a reset button or a way to reset the boiler


some boilers wont reset just by switching on and off, you have to reset to clear the fault

 

[dan_the_plumber]

Yeah there's a reset on the on off switch. You know the ones, you turn them clockwise then they spring back to heating/hot water.

Actually this one was a bit sticky, it didn't really spring back very much. But I mean I could actually see the mechanical parts moving in the PCB when I used the reset switch, so I assume it was working.

 

[dan_the_plumber]

There was no continuity (no tone) across the spark electrode lead. Although I did think after maybe I should have done a resistance test on it because you'll only get a tone if the resistance is less than 1ohm. Also I didn't test the primary NTC for resistance between 12-14mohm, I didn't fancy draining the boiler.
Anyway Alpha told me that if the pumps not running its pointless testing these components. I'm now not so sure. Does the boiler check these components are working properly before or after running the pump. I'm confused.