Janitrol Gas Furnace Short Cycling

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Old 11-19-17, 06:09 AM
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Janitrol Gas Furnace Short Cycling

Hi all,
I've got a Janitrol GMP0753REVB 75,000 BRUHR, approximate age 18 years, natural gas furnace that stopped coming on Friday night, woke up to a cold(er) house than normal. We live in Colorado, so we're getting into the season of below freezing temperatures at night and 40s-50s during the day. House is a 3 bed split level. Thermostat is programmable, but older as well.

So after waking up I tried turning the thermostat switch to off, then back on and the furnace wouldn't kick back on. It's been set to 72 and woke up to 67 yesterday, and 65 this morning. There's a reset button on the thermostat, which after being pressed allows the furnace to kick back on, but it will short cycle for a bit, the fan will stay on for ~10 minutes, and then everything turns off. Got lucky yesterday and the burners stayed on for a while in the morning and warmed up the house.

The only thing that has changed is that I changed out the filter last Sunday with the next level up of "allergen blocking" etc etc, and I double checked to make sure it was inserted the right way. Soo I'm stumped. I want to see if there's anything I can do before I call out a repairman. I'm curious if I'm not getting enough air flow with the the new filter or something. Just trying to keep the family warm :/
 
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Old 11-19-17, 06:17 AM
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Is there a screen that needs to be cleaned on that model? Also, make sure that all the bolts are tight so air can't enter.
 
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Old 11-19-17, 06:20 AM
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The only thing that has changed is that I changed out the filter last Sunday with the next level up of "allergen blocking" etc etc, and I double checked to make sure it was inserted the right way. Soo I'm stumped. I want to see if there's anything I can do before I call out a repairman. I'm curious if I'm not getting enough air flow with the the new filter or something. Just trying to keep the family warm :/
I'd say your problem has been identified. Insufficient air flow is the primary cause of short cycling. Put in a lower MERV filter and your problem may be solved. BTW, there's more to air resistance than MERV rating so you may want to do some research prior to getting more filters.
 
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Old 11-19-17, 06:26 AM
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Yeah I was going to go get the same filter I've had in it previously today and give that a try.
Does that explain the temperature dropping to ~65F even thought the thermostat is set to 72? I figure even if the furnace is getting a signal from the thermostat it won't just short cycle all night trying to appease the thermostat.
 
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Old 11-19-17, 06:30 AM
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Did you recently get an oil delivery?
 
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Old 11-19-17, 06:31 AM
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It's a natural gas furnace.
 
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Old 11-19-17, 06:42 AM
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Sorry about that. In that case, I doubt that it's a filter problem.
 
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Old 11-19-17, 06:53 AM
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I took out the filter to see if that would give an indication of that being the problem, and it's still short cycling. It tried for about ten minutes and has stopped again.
 
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Old 11-19-17, 06:55 AM
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Here's what I'd try next:
  • Check out the registers to see if any are blocked or closed.
  • Vacuum your thermostat.
  • Call for service.
 
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Old 11-19-17, 07:03 AM
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Sounds good thanks everyone
 
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Old 11-19-17, 07:46 AM
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There is an LED on the control board that you should be able to see by looking through the clear plastic hole cover on the lower panel. It normally blinks an error code that that gives an idea of where to start looking.
 
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Old 11-19-17, 08:38 AM
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The heating operation is explained on page 17 with a description of the fault LED flashes.

Furnaces/Goodman_GMP_GMPE.pdf
 
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Old 11-19-17, 01:23 PM
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So it looks like its getting to the step with the flame sensor, because the burners ignite and you can see the igniter de-energize. The burners run for ~4 seconds and shut off. I haven't timed the lockout, but it I'd guess the lockout is occurring because the furnace won't kick on unless I hit the reset button on the thermostat. Bad flame sensor?
 
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Old 11-19-17, 01:35 PM
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Also, after working this afternoon, I heard the burners come on three times and then the furnace shut off. Must be the flame sensor then. Is that something I can get locally or is it only online? Easy to replace?
 
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Old 11-19-17, 02:04 PM
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Here's a picture of the flame sensor. Looks like its carboned over. I've turned off the power and I'm going to try cleaning it off and see if that does the trick.
 
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Old 11-19-17, 02:13 PM
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And removed: Suggested method of cleaning?
 
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Old 11-19-17, 02:56 PM
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Can probably close the thread, I cleaned with steel wool and the furnace ran. I'm going to order a replacement just for fun seeing as they're $10
 
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Old 11-19-17, 03:16 PM
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Really no need for a spare unless you break that one. It's just a piece of stainless steel rod. My choice of cleaner is a scothbrite pad. One of those green ones. Steel wool like Brillo also works. VERY fine sandpaper is ok in a pinch but it's better to not score the rod.

Just polish the rod nice and shiny.
 
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