Testing a thermocouple


Postby musical2 » Thu Mar 08, 2007 8:30 pm

Try a different one? Have bought one - no joy so I'm looking for a little advice.

I've just used a volt meter on both thermocouples - connecting meter leads to inside core & copper casing respectively at one end whilst holding a cigarette lighter at the business end. A very small voltage(millivolts) is present in both thermocouples as they heat up. Perhaps I ought to have done this test before buying another one.

Next I've taken the gas valve out & extracted the bit that the thermocouple screws into. I suspect it's a solenoid as it has a plunger held by a spring. I suspect that by screwing the thermocouple into this solenoid?? & again heating up the biz end, the plunger should operate against the spring and retract into the plastic tube. It isn't doing this anyway so I suspect this part is the faulty one. Taking my multimeter I've checked now this solenoid?? for ohms. If it's a solenoid then it will be a coil of wire & will measure low resistance (inner core to outer screwthreads) It's measuring infinity (highest) which further makes me suspect this unit.

I'm fairly sure I have found the fault here but I'm not a gas engineer (although I am an instrument mechanic) so I'm hoping somebody here will be able to advise me if they can see a glaring :shock: error in what I'm doing.

Thanks in advance,
James
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Postby musical2 » Fri Mar 09, 2007 9:34 pm

Well I've made the boiler work. Won't say how as I'm sure I'll be frowned on but suffice to say I've proved the fault to be within the gas valve. Isolated it now anyway for safety. Can't find a repair kit for the gas valve so I need another unit. Someone may be able to advise here:

It's a V4600C 1029U. I've been offered a V4600C 1466U What's the difference in the last set of numbers and will this valve be okay to fit. Looks the same although I don't have the two sat side by side to check the spec.
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Postby thedoctor » Fri Mar 16, 2007 12:47 pm

MANY OF THE ANSWERS TO YOUR POSTS CAN BE FOUND, WITH DIAGRAMS, IN THE DIYDOCTOR PROJECTS SECTION. CLICK HERE www.diydoctor.org.uk/projects.htm
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Postby musical2 » Fri Mar 16, 2007 7:04 pm

Thanks. I'll bear that in mind. In this case I've repaired the boiler. Was the gas valve. Found another one on Ebay, miles cheaper than elsewhere. Had a good look at it to make sure the pilot light will cut out if it needs to etc.
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