Boiler pilot light goes out when it's cold outside

Hi all,
Got a bit of a weird problem with our boiler. It's a Glow-Worm Economy Plus EP40B (non-combi) with a pilot that should be on all the time.
If the external temperature is above about 0, it's usually OK. However, in the recent cold snap, and after the boiler has been running for a while (so is hot), and about 2 mins after the main burner turns off, I can hear "clunk" and the pilot light goes out.
I had the thermocouple replaced recently, so I think that's OK. (I can always re-light the pilot easily when the boiler is cold, and it will stay on until the end of the next period when the main burner is used).
It seems to be something to do with the difference with the outside air and the boiler temps.
One thing I have noticed is that only the very tip (2mm or so) of the thermocouple is red. Could a draught caused by the temperature difference be "pulling" the flame away from the thermocouple sufficiently to turn it off? Is the thermocouple in slightly the wrong position? Or could the flame not be strong enough (is there any way to adjust it)?
Ideally I'd like to solve it myself, but understand that most things should be done by the pros.
Cheers,
Rich
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On 06/01/2015 11:07, Belperite wrote:

I would say that was it, or something like it. The thermocouple generates enough electrical power to hold a solenoid valve open, but only just. Lower air temperature means it won't get quite as hot, and will produce a lower voltage. Maybe it can be moved further into the flame?

Cheers
--
Syd

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On 06/01/2015 11:20, Syd Rumpo wrote:

That would be my first guess too. Often they are just clamped by a plate and a couple of self tappers, so there should be some positional adjustment for the thermocouple.

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Funnily enough I heard somone say that there is a part of the flame where the thermocouple should sit as its hotter than the rest, I imagine its the bit near the gass/air mixing bit.
All one can do I suppose is play around with it. Brian
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"Syd Rumpo" < snipped-for-privacy@nononono.co.uk> wrote in message
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On Tuesday, January 6, 2015 12:02:50 PM UTC, Brian Gaff wrote:

If the thermocouple is at the hottest part of the flame it isnt gonna last long.
NT
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From my school physics days, when we had bunsen burners, the hottest part was at tip of the blue part.
--
From KT24 in Surrey

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/the hottest part was at tip of the blue part/q
Istr its the inner blue cone tip on a Bunsen flame?
Jim K
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It would be a good idea to clean the pilot housing/cowl first, it can get well crudded up and change the flame shape. It shouldn't be necessary to clean the pilot jet (no poking with pins) as it is usually protected from crud with a cowl.
--
fred
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     snipped-for-privacy@care2.com writes:

+1
They don't normally run red-hot, although there are some double nickel plated ones which are designed for running hotter.
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Andrew Gabriel
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On 06/01/2015 16:46, Andrew Gabriel wrote:

I wondered about that too, but assumed they might be stainless clad, mineral insulated chromel alumel since this is made in large quantities for industrial use. ISTR they are rated for continuous use to around 800 C. They certainly work fairly reliably for 40 years at 650, albeit with a drift of several degrees C because of ageing.
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I've got a very old Glow Worm Space Saver 50 which has a similar problem: t he flame's always close to going out which I think is caused by the cold ai r draft when the main burner is on and drawing fresh air in. Also the main s gas pressure might get a bit lower when it's cold due to more general pub lic consumption so the pilot flame is smaller. Inside the aluminium base of mine there's a pilot flame height adjuster scr ew. The other screw regulates the pressure to the main burner, not to be co nfused. If I were brave enough I might even have a fiddle.
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On 06/01/2015 11:07, Belperite wrote:

I can't really explain the temperature effect which you have seen. Usually, it's just a case of making sure that the pilot flame is the right size and the thermocouple is sitting within the flame.
If you can get at it, remove the pilot jet and clean it by blowing compressed air through it. Don't prod it with a steel needle - which could damage it. In extremis, I have been known to push a strand of soft copper wire through a jet to clean it.
Then check to see whether the height of the pilot flame is adjustable. Some gas valves have a separate pressure adjusting screw for the pilot. You could tweek it up a bit - but don't touch the main burner pressure adjustment.
--
Cheers,
Roger
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Thanks for all the replies guys! I've got some things to go on now. Will probably end up getting an engineer in but have got more things to suggest to him.
Cheers,
Rich
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And if you really wanted to test this theory, you could measure the voltage.
Another possibility is that the solenoid is colder and this somehow makes it require a higher voltage to operate.
-- Richard
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"Richard Tobin" wrote in message wrote:

Boiler thermocouples will typically only produce about 12 millivolts, so really the solenoid is 'current operated' as everything is such low resistance. You'll be hard pushed to measure the voltage difference.
Andrew
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Belperite wrote:

I don't know if your model has one, but ours has a metal shield (called a 'Top Socket', for some reason). Over the years it gets crusty, and becomes unable to point the pilot flame in the right direction. Just needs replacing every five years or so, and the flame is as good as ever.
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Best not to tamper with the flame, best to call out a gas safe approved hea ting engineer. After all they can solve the problem quite easily plus if th ey're as cheap as STL Heating then you won't be paying a fortune either. Yo u could get some quotes in, or save the legwork, time and hassle and use ST L.
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On Fri, 13 Feb 2015 04:52:43 -0800 (PST), snipped-for-privacy@mail.com wrote:

I'd avoid STL like the plague.
They are newsgroup spammers, and apprently need to lie and shill to get work.
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On Fri, 13 Feb 2015 04:52:43 -0800 (PST), snipped-for-privacy@mail.com wrote:
lying newsgroup spam for STL
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