York Diamond 80 cutting off when trying to use heat


Old 09-25-08, 03:54 PM
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Unhappy York Diamond 80 cutting off when trying to use heat

Hello. I did search and did not find the answer I was looking for. I moved into a house which has York diamond 80 furnace. today, it was getting cold so I turn on the heat for the first time and of course, it was not working. I check it out and this is what is happening.

The furnace turns on properly when turning up the temp control, lights up properly and flame starts normal for 45-60 sec, then I hear clicking and the gas stops, then it reignites. This happens several times then it goes into lock out. It is throwing error code #8 which states, bad flame sensor, bad gas valve or low gas pressure. I'm pretty sure it is not the flame sensor as I cleaned it thoroughly and it still happens. Though it could be the gas pressure, I am skeptical as when the flame lights, it is quite strong and does not seem to be low on gas. I've also read that gas valve rarely goes bad. Any idea?? I am planning on getting HVAC tech tomorrow but it is cold!! Any help is appreciated.

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Old 09-25-08, 04:53 PM
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Does the circulating fan ever come on? About the only thing you can do is to make sure all electrical connections are clean & tight. This is especially true for all ground connections.
Old 09-25-08, 05:30 PM
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I doubt it is the flame sensor after that long of a run time. Normally all it takes is 3-4 seconds for the flame sensor to detect.

I'd get out a volt-ohm meter and start checking safety switches, like the pressure switch, to see if there is a problem. If the pressure switch is on the cusp of shutting off, sometimes you can actually see the plunger that goes through the middle of the diaphram move in and out on some of them. A problem can be caused yes by the switch itself, or the tube, or the exhaust pipe (restriction/nest?), or ventor, or for any reason the furnace is not drafting properly. Which can even include a bad heat exchanger.

You also need to determine if for some odd reason, that the thermostat is not shutting off on you. Your first test should actually be in determing that, by making sure the W terminal on the low volt terminal block in the furnace is not being shut off.

Hopefuly your filter is clean, as a restriction can trip out the high limit pretty fast. As one quick test you could open up the blower door, hold in the door safety switch, let the furnace run and see if it runs longer than the 45-60.

Oh. I came back to add yet more: Your symptom can also occur if say an ignition control module is going out. You usually have to determine that by ruling out everything else. This is what recently occured with me with a gas water heater I was working on that is very much like a furnace, including power ventor, pressure switch and ignition control module. I had a hard time believing that since it would fire up that it was the module - but it was. (I should actually review my work log on this).

I never put faith in what those flash codes say they can be. I have found them to be out in left field.

What type of igniton is your furnace, and does your furnace have individual rows of burners or is it the single burner type?
It is getting to be that time of year once again, where all of us guys who have to tend to bad furnaces have to once again put on our thinking caps.

If you need help on testing procedures, just ask.

Last edited by ecman51; 09-25-08 at 05:49 PM. Reason: added more
Old 09-26-08, 08:53 AM
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Hello. Thanks for the responses.

The circulator does come on shortly after the burner lights. My furnace has 5 gas burners and electronic ignition module that heats up to bright red. I doubt it's the filter as I removed the filter all together and it was still exhibiting the same problem. I tried opening all the vents that were previously closed and that did not help either. I checked all the wiring and they are on tightly. I wonder if it's the control module that is acting up.....?

Last edited by joeshmoe12321; 09-26-08 at 10:05 AM.
Old 09-26-08, 05:06 PM
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Here is something you can try without even a volt tester: When it starts to run and you have flame, pinch off the vacuum switch rubber tube and see what that does. You have to squeeze it very tight. If the flame immediately goes out, it could mean the pressure switch is failing (like a leaky diaphram). If the flame keeps running, this could mean that the pressure switch is good, but you are lacking vacuum pulling through the tube, which would mean you have some sort of furnace problem where you'd have to solve why the furnace is not drafting properly.

Or use a jumper wire, with alligator clips (you can get these at electronic stores) and jumper the 2 wires on the pressure switch to bypass it. IF that worked in keeping the flame going, do NOT leave them on, as that test is telling you that you have a safety issue that you have to find why the furnace combustion air is not drafting properly.

Due to the cost of the new ignition module (perhaps $85-$125), you want to rule out everything else that can cause the furnace to shut down. I listed things in my first post. You have to check these. Otherwise there is no sense I even mention them.

Every winter I have to go out on calls to rentals up here in really cold snowbird country and diagnose furnace outages. All kinds of different makes, and lighting and firing styles. And there is a set procedure I have to go through on them including things I have said. I start with the simple and do not take things for granted. I even go back outside and make sure some prankster did not shut off the gas even, (let's say the ignitor glowed but did not fire, for example).You can't leave any stone unturned. Often people would never think their thermostat is ready to turn off, for example, and yet lo and behold, there is something causing the thermostat to short cycle. So you have to check that, for voltage. This is a must test if you have fire, especialy in the range of one minute or longer, and it then goes out! You can't just gloss over these things and pick and choose if you want to quickly solve.


I just thought of another reason how furnaces can run but shut down early. Sometimes this is caused by condensate water that is hung up inside and it affects the drafting. Blow through your condensate line, both through it toward the drain and also back towards the furnace to clear the gook. Thsi should be part of routine maintenance anyway.
Old 10-08-08, 11:29 AM
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OK, so it was finally repaired. It seems like the Pressure Switch was the culprit as the HVAC tech replaced it and it works okay now. He first replaced the flame sensor which changed the behavior a little bit(lights for longer 2-3 min then shut off) but did not cure it so then replaced the pressure switch. It could have been combination of both...who knows.

anyway, thanks for the help!

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