How many millivolts should I get on a healthy thermocouple in Worcester Heatslave Highflow Combi?
The boiler has gone out and won't relight. I can get about 20mv
- posted
17 years ago
Thermocouple - flame failure
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- posted
17 years ago
About right but have you got almost 0 ohms across it at an amp or so? It has to deliver a high current at the very low voltage it generates in order to operate the gas valve's pilot solenoid.
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- posted
17 years ago
I just checked an old one which was replaced last year and it reads 35 mV when held in the gas ring at a dull red temp at the tip. Not much current (2mA), but my DVM is probably high impedance.
john2
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- posted
17 years ago
Not sure that the thermocouple operates the gas valve directly. I thought the mains supply also powered an amplifier.
john2
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17 years ago
The message from john2 contains these words:
Not on the gasvalve I took apart four years ago. Very fine-wound solenoid operated directly by the thermocouple.
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- posted
17 years ago
Replaced now (it failed on Sunday hence trying to fix it). There is no amplifier on any that I have ever seen.
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17 years ago
In message , john2 writes
It's only providing 'hold in' current to the valve because you've provided the initial 'pull in' when you ignited the boiler so it could be said that it's not operating the valve but maintaining its state but it's definitely directly connected with no intervening amplifiers or other such 'gubbins'.
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- posted
17 years ago
I stand corrected, quite interesting though
john2