How do I change the thermocouple on Glow-worm fuelsaver mkII?

My glow-warm 40 mk II failed to re-start after its annual service. The the pilot flame was not staying on after holding in the white gas push button on its pilot setting and releasing it after 20 seconds. The previous year I had to adjust the thermocouple height with respect to the pilot flame so that the flame would hit about 5mm below the tip of the thermocouple. This little trick worked but hinted that the thermocouple was perishing.

This year adjusting the thermocouple position did not solve the problem and I had to change the thermocouple. I installed a honeywell Q309A 900MM type thermocouple supplied by Parts Center, Freemens Common, for £7.90+vat. Robi Robinson gives a pretty good explanation on how to perform the replacement. Here are a few extra tips from my own experience. Separate the assy from the ignitor, pilot, and thermocouple assembly by removing the two 8mm brass screws, support the assy during this operation so not to damage the gas jet at the back or the insulation. The ignitor/pilot/thermocouple assembly will spring away from the main burner. Hold the brown box with the ignitor and the circular see-through window by the front and rotate this 90 degrees clockwise. The brown box will separate from the pilot/thermocouple assembly. Use a lightweight 10mm open spanner to loosen the thermocouple retention nut by turning it anti-clockwise. The thermocouple will detach from its holder. Use the same 10mm open spanner for removing the thermocouple connection to the gas unit. Carefully feed through the old thermocouple tube around the boiler casing without bending it too much to take the thermocouple out of the boiler. Uncoil the replacement thermocouple. Use the neck of a bottle to mould the new thermocouple in the shape of the old one, using the old one as a template, by just running your thumb over the copper tube around the bottle neck. This will prevent introducing sharp bends. Re-assemble the thermocouple/pilot/igniter assembly with the new thermocouple in place, making sure the pilot vee shaped flame holder points straight to the thermocouple tip. Now connect the thermocouple small end with the gas unit. This is an electrical connection, so there is not need to over-tighten the 10mm nut. I found it easier bending the thermocouple tube with the bottle neck so that, from the gas unit, it runs rightwards along the front boiler perimeter, instead of inwards as in the original assembly. This gives a gentler bend to the tubing at this end. The replacement thermocouple is longer, so it is possible to then bend it backwards along the right hand side of the boiler. There is plenty of room at the back of the boiler to let any excess copper tubing length. Make sure the thermocouple tube at the gas unit side does not protrude above the top of the aluminium circuit board case, otherwise you will be unable to replace the aluminium metal front that slides over it. Complete the reverse-assembly as detailed by Robi.

Aldo Rona
July 2011

Fitted a new t/c and the pilot light still ignites but goes out as soon as I take my finger off the ignition sequence button. Could the new t/c be knackered? help please.

Steve W Stockport
July 2009

I hit the same problem; pilot will ignite but not stay on. Tried for 20 secs, as recommended (when the boiler is new, obviously) which failed; tried for 2 then 3 mins, but still failed. Looked around at some sites, including this one. Took off the casing, looked at all of the components that this site and others referred to which made me feel comfortable (that I could see what you'd said I'd see!) Took a look through the pilot window and the thermocouple just looked knacked! Called a reputable local company who came next day for £79 + VAT call out; replaced t/c for £13 + VAT. Job done. Sounds expensive? Well, I've not spent a penny on the boiler for at least 2 years, so that works out about £1 per week; even less than the figures quoted by lots of companies to provide service contracts for you.
So, I'm happy (and clean and warm!)

GoRedSox
March 2009

Not Really An Answer But A Thank You.
I tool the advice for the Thermo Couple for the Glow Worm Space Saver 50 as the pilot went out on my boiler and when i tried to relight it it just would not stay on until i found the Problem listed on this great site.
SO A MASSIVE THANK YOU GOES OUT TO ALL INVOLVED IN THIS GREAT SITE AND FOR THE KNOWLEDGE AND EXPERTNESS GIVEN.

THE TOTAL PRICE FOR THE REPACEMENT THERMO COUPLE WAS £6.00 INSTEAD OF AROUND £200 IF A CORGI MAN WAS CALLED OUT AND HE PUT HIS CHARGE ON AS WELL

PAUL
December 2008

remove lower gold draw cover.
remove centre lower screw from outer cover.lift and tilt cover off.
You should now be faced with an inner rectangular tin cover.This is held in by four screws (bottom and top) remove these and gently withdraw the casing towards you,care because the pipes and cables are behind this.
you can now see clearly the pilot light casing.The casing and the pilot/igniter/thermocouple mounting bracket are held in place by 2x 8mm brass bolts,note support the assy as damage to the gas pipe may occur if too much movement is applied.Remove cover assy, complete with ignitor and support.Gently remove thermocouple (11mm). Trace copper pipe to the other end carefully remove( 11mm)Note black wire to centre is now free to fall out now fit the 900mm universal replacement ,make sure you place all parts on correct way round there is a wasted portion to allow fitment of the collar dont forget black wire fitting is the reverse

robi Robinson
December 2007

Hi, I currently have the same problem in that I cannot get the
pilot light to stay on when I release the button, however I have
only held it in for about 30 seconds or so (so) far. I will try for
a bit longer to see if that helps, but I just held it in untill I thought the thermocouple was glowing as much as it ever was going to (seemingly). I too am thinking of changing the thermocouple, It maybe a relatively simple procedure however
it is not clear if you have dismantled the boiler to any extent
do that you can see the thermocouple. If you have done this
then it appears that it my be a relatively simple to do. The thermocouple is seated in a small housing about the size of a match box, along with the 'pilot light jet' and the 'ignition rod'
so there are three item in all which go into this box. Assuming you have already removed the 3 or so covers which allow you
to get to this area you will notice the 'matchbox bit' is secured to the unit by two small screws on the left handside, when you remove these screws the 'matchbox' is released some what but
still held in place (somewhat) but the 'ignition probe'. I had to
loosen the screw bezel(?) at the bottom of it and pull it down
a bit to remove the cover more completely. Then on the bottom
of the 'matchbox bit' there is small screw which holds the
thermocouple in place. If you loosen the screw (remove completely) you can then withdraw the thermocouple completely. Note the the thermocouple is L shaped not straight
so you can't pull it straight out you need to allow for the L
shaped bit, but it is still fairly easy to withdraw. Then comes the question of removing it from the wire it is attached to.
It maybe you can just pull it out of what appears to be a connector immediately below it, however wire also 'disappears'
into the back of the unit and that may be the correct place to
remove it (I don't know as I have not tried). Even to get this far you have to remove the outer white cover which basicallly pulls out (but there might be a screw (or two) to release first).
Then there is a second metalic box cover which has two screws
at the top and two screws atthe bottom (at least) there may
also be a wind nut. Then there is another panel with 4 screws
in each corner, this could also have the wing nut I spoke of
at the bottom.
I should add at this point that I had a friend who is a CORGI qualified (and British Gas) engineer out (twice) to fix this problem, the first 'fix' only lasted a few weeks, the second
'fix' 3-4 months. I don't think any of the 'fixes' involved changing the thermocouple, I am not sure what he did exactly
I think he may have increased the size of the pilot light by
adjusting a nut at the bottom, however I had a look at that
and I am unclear as to how to adjust it, more to the point am
rather afraid to try incase I cause a gas leak or something like
that however I may try tomorrow. I am aware that such adjustments could be extremely DANGEROUS, you might end up
BLOWING UP YOUR HOUSE, or POISONING YOURSELF WITH DEADLY AND UNDECTABLE CARBON MONOXIDE GAS WHICH WILL
FIRSTLY INDUCE SLEEP THEN *DEATH*.
FOOD FOR THOUGHT!!
I should also add that the thermocouple may not be fauly at all
it could be several other things (gas control valve/magnet) my
gas engineer friend, on the second visit was strongly of the opinion that I really needed a new boiler as the only solution, which he would do at cost price. (so thats an honest opinion not someone trying to make a 'fast buck'), he has done work for free for me in the past, although I have given him a rather inadaquate amount of money for his inconvience, travel and time, If I had called someone out I would probablly have expected to pay many many times what I gave him.
He also cleaned numerous parts of soot and may have made other adjustments I did not notice.
Anyway basically what I am saying is that attempting to fix
gas appaliance when not qualified to do so is an extremely risky
and dangerous business, you could end up losing your home,
your life (and other lives) or both. So ask yourself:-
IS IT WORTH IT?
That is a question I have now asked myself just now. OK I might be able to get it going again but its very likely it will fail
again, probably in mid-winter (its summer now) when I will have
to get it fixed professionally or probably a new boiler which will take some time during which I will have no heating when I really need it (burst pipes?). If the thermocople is failing, which is basically just a piece of wire, what condition do you think
the rest of the system is in?
Basically 'answering' this has helped me to make up my mind that the solution for me (and probably you) is to replace that
ageing boiler!! OK it will cost a bit but new boilers are *far* more efficient and will knock maybe 30% off your annual gas bill. Which gas prices going through the roof it will ultimately
pay for itself. Ref:-
http://www.diybanter.com/showthread.php?t=5004
Having said that I will see if I can replace the thermocouple, they are not expensive parts (if you can find the right one).
If I can find the right one it should be fairly clear whether it is
easy to replace, if so I will replace it. If that doesn't work I will
get a new boiler, I may do so anyway as its fairly clear it will
have to be done anyway as its an old system and they don't
last forever and I don't realy like the though of a freezing week or two in winter without heat!!!!

Edward K.
May 2006