Potterton Suprima 40 loud rattle/buzz noise

[Mike Tomlinson]

Yes, I've got one of those. It was fitted 5 years ago and has given trouble-free service until now.

This morning, the boiler was in lockout (red LED flashing). I pushed the reset button. The green LED illuminated, and when it started flashing rapidly (which I understand is the ignition sequence), a loud, fast rattle/buzz sound came from the boiler. It sounded similar to relay chatter, but louder. After several repetitions, the boiler went back into lockout.

A couple more resets got the thing going so I have heat and HW, but I'd better be prepared to replace part(s). What is making the noise, and what do I need to fix it?

Thanks!

[Mike Tomlinson]

In article , Mike Tomlinson writes

Following up to myself:

I took the RHS cover off the boiler. The buzzing noise is coming from the gas valve. Took the PCB out and found several dry joints on the connector pins and the relays. Resoldered those and refitted. The problem still exists.

Found the Potterton troubleshooting flowchart which says to check for

300v DC on the red and black wires to the gas valve. There's 215V dc on these wires, and using the AC scale, it reads 100v, measured using a multimeter. This doesn't seem right to me. I'm wondering if one of the rectifier diodes has gone on the PCB - does this sound likely?

I'd welcome some reassurance that the problem is the PCB and not the gas valve; if it's the PCB, I'll order a re-con one from Geoff; if it's the valve, I'll have to call in an engineer.