boiler overheating

[Seby]

when switching on my combi it runs fine for a while then overheats so i have to reset it normaly cuts in and out around 60 so i watched boiler till it done it again when temp hit 85 i switched boiler of then back on ran fine no burner on until it hit 55 checked ntc sensor ok thermostat onboard pcb dont want to spend £100+ renewing it without being sure

Thanks

 

[micky p]

when switching on my combi it runs fine for a while then overheats so i have to reset it normaly cuts in and out around 60 so i watched boiler till it done it again when temp hit 85 i switched boiler of then back on ran fine no burner on until it hit 55 checked ntc sensor ok thermostat onboard pcb dont want to spend £100+ renewing it without being sure

Thanks

which boiler is it.

 

[esra_ptrap]

It's the steaming clanking one in the corner I'd guess

 

[ChrisR]

The one which needs some full stops?

 

[Seby]

valliant vcw-sine 18 t3 w approx 20 years old

 

[Agile]

If the NTC is really OK and the boiler is not controlling the temperature then the control PCB would be expected to be faulty.

However they are pretty reliable but like anything they can fail. There are lots of interconnections!

I seem to remember I saw one where the OC28 or similar transistor had failed but I dont remember what the failure mode was in that case. Possibly the same as yours.

Tony

 

[Seby]

thanks Agile will replace pcb will post back results

 

[micky p]

If the NTC is really OK and the boiler is not controlling the temperature then the control PCB would be expected to be faulty.

However they are pretty reliable but like anything they can fail. There are lots of interconnections!

I seem to remember I saw one where the OC28 or similar transistor had failed but I dont remember what the failure mode was in that case. Possibly the same as yours.

Tony

do pcb's go down on vaillants Only ever replaced 1 PCB on a turbomax once.

 

[Agile]

A professional would only change a PCB when everything else had been checked as OK.

This would include checking the gas valve setup which should be difficult for most DIYERs.

Tony

 

[carlosg]

hi seby - i have same boiler & same fault. Can you let me know if pcb was faulty or something else?