I have a Glow worm Economy 50 CH boiler and I cannot get the pilot to stay lit. I have tested the circuit according to the instructions in the book and I think the thermocouple is OK as I get 14mV when the pilot flame is lit. I am uncertain what the unit in the gas valve itself does (this is the screw-in unit that the overtemp stat wire connects to). It is a small electro magnet with a spring loaded plunger. I have tested it with a 1.5v battery and if I push down the plunger, the magnet will hold it. I cannot see how the thermocouple will generate enough power to do this though. Also, what is supposed to compress the spring in the first place?
I have tried to get the pilot to stay lit by removing the spring plunger, but it still goes out when I reklease the manual button.

Will Timbey, July 2006

Never get too technical with gas valves, it doesn't always work like the instructions state; especially when old...

You compress the spring to allow gas to pass though the pilot tube when you depress the big button on the r/hand (If memory serves me correct) of the gas valve (Should be made of plastic)... This then pushes the valve seating onto an electro-magnet, energised with the thermocouple's heat from the flame... If the thermocouple is in good condition and everything is nice and tight, then you'll probably find it is the overheat thermostat gone (The little plate with two wires on it that sits between the thermocouple and the rear of the electro-magnet on the gas valve)...

YOU MUST BE CORGI REGISTERED TO CHANGE THIS COMPONENT!

You may still get continuity on this component, but it will be a false reading, 99% of the time, if the thermocouple is good, then it will be the over-heat thermostat... Should be around £4 trade for this appliance.

ccMods, July 2006