York Furnace Intermittent No Heat Issue


Old 01-02-17, 02:59 PM
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York Furnace Intermittent No Heat Issue

I need some input and advice about an intermittent furnace heating issue we started encountering yesterday. It isn't consistent so it's been hard to diagnose.

Yesterday morning, we noticed that the heat wasn't being turned on to reach the set temperature. We had it set at 66 degrees and when we woke up it was about 61 or 62 according to the thermostat. I was able to get the temperature up to about 65 or 66 and noticed the blower continues to operate but the gas stopped and the flames went out thus cold air was being blown out the vents.

I turned off the furnace at the thermostat and at the switch on the outside of the box and checked the filter. Realizing I was overdue with replacing the filter, I swapped it out with a new one and tried to run the furnace again. This time the heat would only work for about 5 to 10 minutes. I shut it off again but had noticed that I was getting 4 flashing lights. According to the label for my furnace, 4 lights means "high aux. or spill limit switch open."

I've done some searching online trying to find some info and ended up cleaning up the thermocouple that was replaced maybe 2 years ago. I cleaned it up and powered on the furnace. I also attempted to use the reset buttons on the 3 roll out switches inside the furnace.

It operated all night holding the temperature at 66 overnight until we returned home from skiing this afternoon and it had dropped to 64 and only the blower was working. No heat. I noticed the lights were flashing again. It was then reading below the set temp. I shut off power again for about 5 or so minutes, turned it on and the lights continued to flash. I shut it off again and checked for continuity on the primary limit switch and the 3 roll out switches located inside the furnace box. All 4 total switches measured at about 0.2-0.5 Ohms and the continuity indicator sounded each time I measured it. I hooked the switches back up and pressed the reset buttons on the 3 roll out switches. After a few more minutes (probably 20 minutes total of power being off) I turned the power back on to the furnace and turned the thermostat back on. It worked without issue bringing the temp from 65 to 66 and as I'm typing this I bumped up the temp to 67 and it is currently working without issue.

I'm not sure what to check for next short of calling in a technician to evaluate it. Any advice? Thanks in advance.
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Old 01-02-17, 04:19 PM
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Welcome to the forums.

You are not getting a rollout issue so don't mess with them.
You are getting a plenum overheat.

The board is going into safety shutdown and every time you turn the power off you're resetting it.

Typical things to check.... dirty filter, too many registers closed down, blocked returns, dirty A/C A coil, dirty blower wheel and last but not least.... cracked heat exchanger.
Old 01-02-17, 04:37 PM
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The filter was replaced yesterday so it shouldn't be the filter. We haven't changed anything with how many registers are opened or closed and it was working fine prior to yesterday morning. I'll check the blower wheel. How do I check the A/C A coil?
Old 01-03-17, 08:41 AM
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To check for blocked evaporator coil (AC) try and follow the copper tubing going from your outside AC unit to the furnace, where they enter the furnace is where the evaporator coil is, post a pic and we may be able to assist in locating the cover to remove.

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