Hi All,
I had another look at Mums 'old but going to br replaced soonish., the pilot won't stay alight' Ascot / New World (Main?) gas boiler again yesterday and think I found the upper limit cutout / inhibitor (?) had triggered? I pressed what looked like a rest button in the middle of it but as didn't have any real tools / meter with with me (only the trusty Leatherman as always) I couldn't measure anything so shorted the extra stat out (for testing) and tried to light the pilot.
Hold in the contril knob, hit the piezo, nice little pilot flame, hold knob in 30 seconds, release, pilot stays alight (hah huh, so it was overtemp cutout ..?).
Turn the gas knob round to 'On', pilot goes out?
Wait 3 mins, relight pilot, turn knob to 'On' pilot stays on this time, turn mains power to boiler, main burner lights up but then main pilot and burner goes out? Try this a few times with similar (intermittent) results. So, it could just be that the thermocouple was 'marginal' and as they are 'cheap' ....
So, I removed the thermocouple (amazing what you can do with a Leatherman PST) and this morning picked up a replacement. It's not the 'correct' part (long since obsolete) but sufficiently close where it matters to 'do'.
I just did some comparisons between old and new probe using my DMM and the gas stove and noted the following with either (probe, not DMM) in the gas flame (simulating pilot).
New device .. open cct voltage 30mV, short cct current (DMM on 2mA)
250uA.Old device .. 23mV and 200uA ?
So, from that very crude test the old thermocouple isn't 'dead' but maybe down on performance (especially when not in a 'strong' flame ie only a 'pilot' not a low gas ring) enough to make a difference?
I'll see what happens when I , sorry, 'the Corgi bloke', put's it back later... "You know anything about parachutes ...?" ;-)
All the best ..
T i m