Suprima 50 Gas Solenoid Valve Clicking After 10 mins.

[freddig]

Hi folks,
I've got a Suprima 50 with the new type PCB (Installed 2 years ago). Boiler fires up runs for about 10 minutes (flow good, pumps runs fine). Then the Gas Valve starts clunking (several times in quick succession), the boiler restarts, but shuts repeats process soon after. No lockouts and it's still got external call for heat. Checked the PCB, still in mint condition, no sign of dry joints or heat scorching. Any and all help would be appreciated.

fred.

 

[Dan Robinson]

Call a professional.

 

[Agile]

Who fitted the new PCB ?

Tony

 

[freddig]

Hi Tony,
Previous owners had it fitted, but neighbours told me the old owners had "boiler circuit board" problems about 8 months before we moved in; so roughly two years ago! I'm a professional electrical and electronics engineer of 28 years (who knows his limits!), working on large electrical system down to component level electronics, so knowing that the PCB was often No.1 suspect, I thought I'd do a little electrical diagnostics before calling in the Gas Pros!
The thermistor reads about 900k at Room Temp, haven't tested at a higher temp yet, but if this failed open I'd assume the boiler would keep heating until the OH tripped (unless the circuit has open-circuit detection). I'm guessing the Gas Valve/Solenoid has been changed at some point as there is signs of black scorching on the inside of the right removable panel. I know it not recent because it's partly under the sticker for the new PCB layout!! Again any help would be appreciated!


fred.

 

[Agile]

PCB would recognise open circuit NTC.

It has to so it can avoid producing too much heat.

Tony

 

[freddig]

That make sense, Tony. When it shuts down after about 10 minutes (and a few sol clicks), I get the standard Flashing Green (boiler at temperature) LED. I know this new board has LED fault modes for Thermistor/Overheat/APS fault, but I get none of these it just restarts. Have you any knowledge of faulty Thermistors/OH sensors causing spurious problems that aren't detected by the board?

 

[hertsboilers]

Surprised that, if you are an electrical and electronic engineer, you didn't take a multimeter to measure the voltage to the gas valve?

 

[freddig]

Yep, did that already, it was about 250V DC whilst running then dropping to 0V when it cuts out! So making sure something else isn't triggering the shut-down.

 

[hertsboilers]

If its flow temperature reaches the setting ie 70C or 80C for example the boiler will stop without any lockout flushing.

Is the flow pipe very hot when boiler is being stopped? If yes, check the circulation.