I won't go into the saga of how I've arrived at having to ask this question (see QUESTION below to cut to the chase because yes, I have gone into a bit of the saga), but an HVAC service guy who is probably excellent for 99% of his calls had a rough day installing a new Gas Valve on my old furnace. What I think is called a "flue limit switch" had additionally fried, related-to or coincidental-to the gas valve's pilot valve sticking open sometimes, which was the initial problem.
The flue limit switch (shown as maybe OPT on the schematic?) was a smallish plastic thing that once fried, really put out an intense chemical odor (like melting plastic). It sat above all the burner stuff mounted to the round blower housing in its own little sheet metal box, and from what the tech explained, what it does is makes sure there isn't too much heat, and shuts off the burners if there is.
Well, he was going to order its replacement, but in the meantime connected the wires, bypassing the switch, so he could complete the furnace work at hand and get it functioning. Unfortunately he connected the wires exactly wrong, so for hours he was convinced that once the pilot was lit, the sensor was not "rectifying flame", and that's why it would all shut down.
I kept trying to point out that the shutdown was happening way fast (like right away after the pilot lit) compared to how long it previously would seem to "try" to rectify that there was flame before turning the burners on. Finally I guess I said it the right way, pointing out that it was as if that flame check is happening and then some further check is not passing its test, and I pointed up at the jumped wires for that fried/removed piece.
Okay, sorry to have told so much of the saga, but early on he had said that he, as a licensed HVAC guy, couldn't connect those wires to bypass that safety switch, so we basically had a "wink wink" agreement that I connected the wires to bypass the flue limit switch (if that is what it's called). Anyway, when he switched them after my suggestion and considering the schematic again, all worked fine and the plan was that he'd get the part and right after the holidays come back to install it.
Bottom line now is that the part isn't available, and they (local company he works for) sent their invoice (I called several times in January saying there's supposedly a part still on order, and pointing out that I hadn't paid them a dime yet), and on the invoice it reports "system operating safely" and "replacement optional switch is no longer available".
QUESTION: How does this sound to the experienced HVAC people here? Do you recognize that function/positioning of such a switch? ("Flue limit switch" is just the phrase I found online, but seems to be it.) If you do know this backup safety switch, is it something that experienced people would say can be removed and the furnace is still safe?
Or should I not trust the local company saying it's safe and pursue maybe a generic replacement (since the exact isn't available)?
The end of the saga for the service call, of course, is that even a good tech who has a bad day gets pretty expensive, and in his flailing I did also get to buy an ignition control I'm convinced was never a problem. (A universal one from his truck didn't get it to work, and then when he went to the parts store and that ignition control didn't get it all to work either, with all still behaving exactly as my ignition control - which had always lit the pilot - had been. I know the parts store, and there are no returns. Again, switching the jumped wires bypassing the flue limit switch is what got it all working.)
Any insights appreciated, but I won't be able to supply a photograph of the fried and smelly little part 'cuz the tech took it with him...
Thanks,
Rich
The flue limit switch (shown as maybe OPT on the schematic?) was a smallish plastic thing that once fried, really put out an intense chemical odor (like melting plastic). It sat above all the burner stuff mounted to the round blower housing in its own little sheet metal box, and from what the tech explained, what it does is makes sure there isn't too much heat, and shuts off the burners if there is.
Well, he was going to order its replacement, but in the meantime connected the wires, bypassing the switch, so he could complete the furnace work at hand and get it functioning. Unfortunately he connected the wires exactly wrong, so for hours he was convinced that once the pilot was lit, the sensor was not "rectifying flame", and that's why it would all shut down.
I kept trying to point out that the shutdown was happening way fast (like right away after the pilot lit) compared to how long it previously would seem to "try" to rectify that there was flame before turning the burners on. Finally I guess I said it the right way, pointing out that it was as if that flame check is happening and then some further check is not passing its test, and I pointed up at the jumped wires for that fried/removed piece.
Okay, sorry to have told so much of the saga, but early on he had said that he, as a licensed HVAC guy, couldn't connect those wires to bypass that safety switch, so we basically had a "wink wink" agreement that I connected the wires to bypass the flue limit switch (if that is what it's called). Anyway, when he switched them after my suggestion and considering the schematic again, all worked fine and the plan was that he'd get the part and right after the holidays come back to install it.
Bottom line now is that the part isn't available, and they (local company he works for) sent their invoice (I called several times in January saying there's supposedly a part still on order, and pointing out that I hadn't paid them a dime yet), and on the invoice it reports "system operating safely" and "replacement optional switch is no longer available".
QUESTION: How does this sound to the experienced HVAC people here? Do you recognize that function/positioning of such a switch? ("Flue limit switch" is just the phrase I found online, but seems to be it.) If you do know this backup safety switch, is it something that experienced people would say can be removed and the furnace is still safe?
Or should I not trust the local company saying it's safe and pursue maybe a generic replacement (since the exact isn't available)?
The end of the saga for the service call, of course, is that even a good tech who has a bad day gets pretty expensive, and in his flailing I did also get to buy an ignition control I'm convinced was never a problem. (A universal one from his truck didn't get it to work, and then when he went to the parts store and that ignition control didn't get it all to work either, with all still behaving exactly as my ignition control - which had always lit the pilot - had been. I know the parts store, and there are no returns. Again, switching the jumped wires bypassing the flue limit switch is what got it all working.)
Any insights appreciated, but I won't be able to supply a photograph of the fried and smelly little part 'cuz the tech took it with him...
Thanks,
Rich