On 17/12/2020 03:08, Chris French wrote:

Our gas boiler has decided of course that this is the week to breakdown

It's an Ideal Mexico Super CF4120, this is a floor standing open flued boiler,
it's a pretty basic boiler with nothing in the way of fancy electronics. The
only control is water temp thermostat.

(drop me an email if if you need a copy of the install/service manual
for this boiler)

There is also a down draft detecting thermostat near the base of the
flue inlet as well. That is designed to cut power to the boiler if
there are adverse weather conditions that would risk pushing combustion
products out into the room. If that fails open circuit, then the boiler
will not fire. (you would get no spark either - since its inline with
the boiler power supply).

When required to fire up, it has a pilot ignited by a spark , which then
lights the mian burner.

So it stopped lighting up. Though I could hear the spark clicking.

I presume the pilot is not lighting either?

As I've done a couple of times before when this happened removed the burner
unit and gas the pilot light burner and igniter a good clean and blow out
with a compressed air can. Unfortunately this did not sort the problem :-(

The gas valve is one of these

https://www.tradeboilerparts.co.uk/I...Part-no-170664.

I've tested the solenoid resistance on the left with my cheapo multimeter at it
is showing open circuit , so has presumably failed. Are there any other checks
I should do?.

I would verify that mains voltage is appearing on the contacts when the
controls are calling for heat - that way you eliminate any other
possible cause in the controls prior to that point.

Or is that pretty conclusive?

As long as there is actually gas getting to the valve, yup.

I don't know much about the gas valves, does the
solenoid control the flow of gas to the pilot as well?

On this boiler there appears to be two live connections to the gas valve
- one presumably for the pilot and another for the main valve. The PCB
may sequence these, and possibly turn off the pilot once the ignition
electrode detects the main burner firing.




--
Cheers,

John.

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