Glow-Worm 85-100 pilot light going out.

[Impecunious]

Pilot light was going out every month or so, so the immediate assumption was the TC. However before changing this, I had a look at the spark electrode. After 30 years of it sitting in the pilot light a lot of it had corroded. It should loop over and present itself about 5mm from TC but mine didn't. Fitted a new electrode, which sits in the pilot, glows red hot and I guess that some of the IR radiated from it helps to heat the TC. So before rushing to change TC, check electrode. If you need to check TC, its output in gentle heat should be 15-20mV. Voltage to hold pilot valve open about 8-12mV, so lots of headroom.
Also, minor water leaks can be self sealing. about 12 years ago it started to weep along output manifold joint, but within a couple of months it must have rusted up, sealed itself and it has been bone dry since then. Isn't cast iron wonderful ?

 

[gas112]

PMSL the heat from an electrode is help keeping a pilot established on this boiler

 

[Dan Robinson]

I'm assuming there is a point to the 0P ?

 

[Steelmasons]

Jeez........what a clown.

 

[Impecunious]

Apologies if the point of the post was not made clearer. It was to state that before condemning the TC (Thermocouple) it may be worth looking at the spark electrode (device designed to discharge a high voltage and ignite the the pilot light) to see if it is worn (I'm sure you can work that one out for yourself :-] ). Also included in the post were a couple of voltage readings that may help anyone who wished to check what they should be getting from a TC (see above).

Additionally, it was a celebration of the fact that the boiler is still functioning pretty much as intended by its manufacturers, 30 years after its construction. A tribute to its design and engineering, admittedly in the days when the gas was coming in fast and cheap from the North sea.

As for the IR from the electrode, I'm simply concluding based on evidence. TC unmoved and unchanged, the only variable was the new electrode and the pilot now remains alight. Could even turn down the pilot jet on the Maclaren
Hope this has helped you understand the reason for the post. ;-]

 

[45yearsagasman]

Your technical advice on thermocouple outputs and the ignition electrode is absolute ball cocks.

 

[Impecunious]

Please advise what is the correct voltage for a TC. Using high impedance DVM (input impedance 10Mohm) the output I was getting was between 15 and 25 mV. Tests on a Maclaren for this boiler showed it would hold above 10mV, with a current of around 300ma. If you think these are widely off the mark I will go and retest
What are your figures ?

With regard to the IR from the electrode, you may be right in that the flux density is not great enough to make any significant contribution to the irradiance on the TC. I'm simply stating opinion based on observation and am prepared to keep an open mind on the matter.

 

[Steelmasons]

What you fail to realise is the fact you possibly disturbed a partial blockage to pilot injector when replacing spark electrode.

Spark electrode has no bearing whatsoever on TC/TEV .

I suggest you keep a closed mind on the matter.

 

[Impecunious]

Thanks for making the first sensible contribution. There is the possibility that I disturbed the pilot during the operation, however the size and shape of the the flame before and after the change were more or less identical. The TC was relatively new and sitting well in the flame before the change and the electrode replacement didn't require me to disturb it or the pilot jet. It was the newness of the TC that made me think the problem could lie elsewhere and look at the electrode. ( Yes I know that new items can fail early) Just perhaps as you suggest, there may have been somethinbg sitting on the jet that was dislodged by unbolting the electrode, but as I say, the flame had an identical appearance before and after. But thanks for the idea.

45years, I eagerly await your figures for a TC, with so long in the business, surely you can reel them off in an instant.

 

[Dan Robinson]

 

[Steelmasons]

45years, I eagerly await your figures for a TC, with so long in the business, surely you can reel them off in an instant.

He would nail you to the floor so don't bother going there.

 

[Dan Robinson]

Go easy on the poor chap Steel - being Impecunious, he probably has little else to entertain himself .

 

[Steelmasons]

He would nail you to the floor so don't bother going there.

2nd useful contribution.

 

[Impecunious]

Nail me to the floor ?
In the same way that he puts his pipes in ?

And thank you Dan for your concern as to my hobbies and pastimes. I do have some... many in fact, but I must say that of all the dating sites I've been on, this is the worst.
I'm going off now to humpquick.com.
It's been almost a pleasure writing to you ... and steel. Thanks.

I would put a couple of smileys in, but they don't seem to work properly

 

[Impecunious]

Oh yes, they seem to.