[West Hill Tom]

Hi there, I'm new to this group so thanks in advance for any help you can provide. I'm trying to trouble shoot a York Diamond 80 that starts, ignitor starts, and then when flames kick on, it shuts off. It should be the flame sensor, right? I've replaced that but the problem persists. The issue when it occurs, is mostly after the furnace has sat for a period of time (like overnight when the thermostat is turned down). Most of the time when it happens, as soon as it shuts off, the furnace comes on again and usually works the second time. Lately, though, when it shuts off, it doesn't come back on at all unless I physically turn the switch on the thermostat off, then turn it back on. I've done a lot of looking online but can't seem to find this same problem. Any ideas? Many thanks!

 

[eggs]

There is a control board that should flash a code when this happens. On the inside of one of the doors will tell you what the code means. More than likely, if you know the flame rod is good, then it is the air switch. This will open as soon as gas starts flowing because the secondary exchanger has water in it and there is very little air flow. FIRST - TAKE PICTURES. So many times people take things apart and forget how to put back together. You need to remove hoses and clean the out. The hose to the exchanger can get plugged or plugged just inside the exchanger. Mouth pressure is enough to clear. There is a drain trap that also can get plugged up, it needs to be cleaned. NEVER blow pressure into the air switch, you will damage it. This resolves 90% of the issues on 90% off. furnaces. Assuming your is a 90% unit.

 

[markusolas]

There is a control board that should flash a code when this happens. On the inside of one of the doors will tell you what the code means. More than likely, if you know the flame rod is good, then it is the air switch. This will open as soon as gas starts flowing because the secondary exchanger has water in it and there is very little air flow. FIRST - TAKE PICTURES. So many times people take things apart and forget how to put back together. You need to remove hoses and clean the out. The hose to the exchanger can get plugged or plugged just inside the exchanger. Mouth pressure is enough to clear. There is a drain trap that also can get plugged up, it needs to be cleaned. NEVER blow pressure into the air switch, you will damage it. This resolves 90% of the issues on 90% off. furnaces. Assuming your is a 90% unit.

He says he has York Diamond 80!!! It’s old 90S furnace!! . Inspection of heat exchanger needs before even fixing anything else since it’s old.
Probably pressure switch or flame sensor or something.
What is serial number on it? If it’s 30 years old maybe time to replace it