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Question DetailsAsked on 11/11/2016

piolet light vstays on but unit will not kick on replaced thermocouple now piolet will not stay lit

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2 Answers


it is after midnight, so rather than try to expalin the possibilities in detail, I am going to lay the burden on you to do a bit of reading of several prior similar questions with answers linked below - pick and choose through the descriptions for the case that fits your original situation (though it might have just been a thermocouple gone out, as they do every few years or so). Could also be one of five likely or common causes after the thermocouple changeout (actually ended up listing them in from probably least likely to most likely, so read/consider in reverse order) -

1) the thermocouple is bad - getting more common these days with new ones, I hear about it and experience it unreasonably often - one reason I stay with Honeywell although I have had a couple of new Honeywells be bad too. You could try getting another one of correct rating and length and try it - even if that turns out not to be the problem, you end up with an extra for maybe $10 or so, just keep so you have a spare next time.

2) you did not get the thermocouple properly making contact up inside the gas control valve. The silver button on the end of the tubing has to make contact with the contact point up in the recess. Straighten out the last 3-4 inches or so of the tube so it will feed in straight, slide the threaded nut down the tube out of the way, slide the "button" end up into the hole making sure (compare by marking the tubing with a felt pen at the length a wood sliver will go up into the center of the hole) that the button makes it all the way in - common for it to hang up on the threads, especially if tight up against the threaded nut and the tube is a bit cockeyed so it hangs up going in. Then when it is all the way in, hold the tubing snugly in place and slide the nut up to the threads and gently tighten it. Do NOT mash it down hard - will flatten out the button and can short out the thermocouple.

3) if yours is the common type where thermocouple and pilot and the pilot (or pilot and burner) gas tubes come out together as an assembly, that tubing is now full of air when you put it back in, so while holding the ignitor flame in place (or pushing the piezoelectric ignitor button) you have to hold the gas control knob in the light pilot position (usually at Pilot setting and pushed down) for 5 seconds to as much as a half minute or so with some models as the gas fills the pilot tube and finally ignites. This would be if the pilot does not light at all after reassembly.

4) if the pilot lights but will not stay lit (after you have held the light pilot button down for the 30 seconds or so of pilot flame it takes to heat up the thermocouple and keep going by itself), then likely the thermocouple is not directly in the pilot flame correctly - 1/3 to 1/2 of the tip should be directly in the blue flame (which might put the very end at the tip of the blue) - see owner's manual or lighting instruction on the label on the side of the tank for exact configuration. If the thermocouple does not get hot enough from the pilot light then as soon as you release the button the gas control valve it thinks (because it is not getting electricity from the hot thermocouple) that the pilot went out, so it shuts off the gas flow.

5) some water heaters and boilers will not light properly (some will light but the control box prevents it from keeping burning) unless the temperature dial is set to the lowest setting. The theory is to not have the burner possibly kick on while your hand might be in there lighting the pilot or your face is right up against the open access port.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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