Gas boiler not lighting - Gas valve?

Sounds it.

Mine's a permanent pilot, and yes the solenoid valve supplies it (controlled by thermocouple) ... hope my gas valve keeps hanging on in there ...

Classic symptoms of the thermocouple failing. To light the pilot light you manually override The pilot light heats the thermocouple

Ignore - I pressed send instead of delete.

failed.

High up the list that's for sure.

This boiler doesn't have a permanent pilot. Logic/safety would suggest that the gas for the pilot is not supplied without incoming mains and the spark generator running (possibly with a time out). Once the pilot lights it heats the thermocouple that operates the main gas valve solenoid. Loss of mains causes the main and pilot gas valves to close shutting of the boiler and pilot.

In theory... See if the service manula can be found on the 'net to find out how/what it is supposed to be doing.

(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).

I presume the pilot is not lighting either?

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.

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

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.

After checking power is getting to at least one of the solenoids on the gas valve you might be able to do the following.

I don't know the layout of this boiler but if the pilot is blocked, or the pilot solenoid side faulty, it may be possible to use an extended gas lighter to heat the thermocouple for the main burner to then light.

Thanks for the offer John, I have a copy.

Yup, I discovered that one windy winters night :-)

Nope

Yep, got voltage

Yep, disconnected the union to check for gas.

Yep, that@s exactly what seems to happen

Thanks John

Thjanks Dave, yeah I've got a copy of the install and maintenance manual.

That's the gist of it, but This one doesn't have thermocouple. The spark electrode acts as a sensor for when the pilot is alight. The PCB then opens the main gas valve.

In which case, I would have to concur, shagged gas valve...

(have seen this on other mexico boilers - although normally the manual pilot type. One that failed to fire at all, and one that failed shortly after main burner ignition as the valve warmed up).

Its an odd design in a way - more sophisticated controls (spark ignition etc) that many mexico models - but not room sealed...

It hasn't lost it's earth (as in real) has it? Don't know the mechanisum but there are post mentioning boilers not starting when run from a genset that doesn't have neutral tied to earth somewhere.

That's for ones that use flame rectification to sense ignition. Even when that mechanism fails the main burner will still light, but then it fails to "prove" and the controls shut it off again.

Is there much point, given the solenoid valve is known to be O/C ?

Wouldn't the main solenoid be OC unless the pilot solenoid was engaged? The fail safe lot get very fussy about gas...

Ok, new gas valve on it's way.

A couple of small queries.

The boiler manual says of the pressure testing points on the gas valve, to loosen the scews in them to test the pressure. Except there are no screws in them, just a threaded hole.

I presume I need to use a pressure test nipple in them? Are these likely to be the common 1/8 BSP size? I can't find any info on it .

Is the feed pipe likley to be hard to remove? It's threaded in and the other end is the female part of the union, so no nut or anything to use a spanner on?

Thanks

I have never tried it on one of those, but I would expect so.

IME yup it takes a fair amount of oompf to get it free (taper steel pipe thread into ali casting ISTR). On the bright side there is usually a bend in the pipe, which gives you some leverage. However gas valve clamped up in a vice and a big stilson wrench on the pipe will do it (YMMV). Refitting is much easier I expect!

Unfortunately, just a short length (20cm?) of straight pipe.

On the brightside I do have a big FO lighweight stillson wrench left behind by the chaps who changed the gas mater a few years back :-)

Thanks John

Chris ?French snipped-for-privacy@familyfrench.co.uk> wrote in news:part1of1.1.z3r6# snipped-for-privacy@ue.ph:

Are the threaded holes in the cast-in posts on the gas valve?

If so I'd expect the screw to be deeply recessed within the posts and the posts to be sized to be a fit for the manometer hose, no nipple reqd.

That's certainly the case here but mine's not an ideal or mexico.

No need to remove the screw, just open a 1/4 turn or so as no major flow reqd.

No. It's just a coil of wire with a finite impedance. If the impedance is infinite, it's stuffed!

Depending on the gas valve, the OP may be able to buy a new coil without having to replace the whole valve.