The furnace short cycles. diagnose the problem. #1 Answer

This is the answer to the short cycling gas furnace. This video is part of the heating and cooling series of training videos made to accompany my websites: and to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

23 Replies to “The furnace short cycles. diagnose the problem. #1 Answer”

  1. What would cause the thermostat to start smoking and burn out? I literally got smoke coming out when I adjusted that anticipator to the right almost all the way. The thermostat is connected between a Taco 555-050RP powerhead and a Taco ZVC 405 control. Amp draw on powerhead is rated at .9 amps. I did not expect adjusting the indicator all the way to the right could cause it to literally burn out. Is this possibly a problem with a failing powerhead. I will replace the stat and powerhead just to be safe.

  2. You explained the problem but you don’t give a solution. How do you adjust it? It would have been nice to show that.

  3. Thank you so much for this video! Can’t believe the feeling of being able to enjoy a warm house again. GrayFurnaceMan you are the man. Blessings

  4. Hmmn.Im trying to find out if this is my issue.I have the same honeywell thermostat.I just had the blower motor and filter replaced on the 30yr old Armstrong furnace.Not seeing any error codes.The pilot comes on and it starts blowing,but the temperature in the house wont go over about 62.Ive tried turning the thermostat up to 80, but it will just run and run but it doesnt show(or feel) a warmer temp in the house.The vents in the hall dont blow warm air,maybe they arent supposed to idk..thats why I'm here looking for insight,lol.I cant afford to have the thing running all night/day and not actually getting it up to temp.Ive had to turn the thermostat back down to get it to shut off.The anticipator is set at .4 im not sure if its been messed with but everything seemed to work fine last winter.Id appreciate any tips or ideas,thanks for your time!

  5. The Anticipator must be matched with the gas valve. Look on the gas valve and a value will be stated there. Match it with the thermostat by sliding the pointer to said value.

  6. I dont want the thermostat to heat itself can you shut the internal heating completely off … my central heat sys. needs to run non stop until the desired temp or else the desired temp will not be reached… and it will stay cold in the room…

  7. I have a Problem with my thermostat please help!!! I have this exact model thermostat in my apartment. We have terrible insulation and the bedroom is above the complexes boiler room. As you can imagine the bedroom is always hot while the rest of the apartment is freezing, aside from that, my problem is that 1. The heat is either blazing, or not on at all, there is no inbetween and if it's on, it is very difficult to get it to shut off and the same when it is off and I want it to turn on. 2. I don't understand what you are talking about. If you could explain what each thing is and how it works, I'd appreciate it.
    The Last 2 days the heat has been pumping non stop and I had the dial on 50. The bottom temp number was reading that it was 78 degrees In the place. I finally discovered that metal bottom piece with the tiny ticks and noticed that it's pointer was all the way to the right, so I moved it all the way to the left, and finally it seems as though the heat is now off. I'd really just like to make it work properly though. Can you please help? Thanks!

  8. Seems like lots of videos sometimes have sound volume problems. I use headphones while the wife has the TV going and can pump up the volume comfortably. I use an IPAD so it has a small built in speaker anyway.

  9. Just thought I'd let you know. I was having a short cycle before a continued reheat cycle, forced hot water by oil, mercury Honeywell thermostat. Over the years I've messed with the anticipator to no avail. I just replaced both with new electronic thermostat and the short 1-2 second cycle, off, then back on was eliminated. All running superbly. Thanks, for being out there. GFM

  10. so if you suspect this is the case is it just a simple matter of twisting the wires together after removing the stat to see if it runs correctly or no ?

  11. Thank you grayfurnaceman! After spending thousands of dollars paying for my furnace repairman to replace fan limit switches, inducer motors and adjusting the fan limit switch I watch your video and found out that the anticipator on the thermostat. wasn't to fine tune the temperature on thermostat that it adjusted when the when the burner would go on and for how long. I did the test like you said to turn the thermostat all the way up to see if it eliminates the short cycling and it did. I called a new company and asked them to adjust the amperage on the anticipator to the amperage that was being drawn so it would work correctly so after 6 different bills all it needed was a simple adjustment. unfortunately I'm not getting a refund for all the parts changing that my furnace man did. but at least now we are comfortable. That jerk even tried to convince us that we need a new furnace. Thanks again grayfurnaceman for keeping us consumers informed.

  12. on my Beckett oil furnace I replaced the limit switch because it was sticking but didn't seem to fix it completely. it heats up kicks on fan and in just a few seconds it kicks off the fan. burner stays on the fan comes back on and off limit switch is exactly the same as the one that came off it neither one of them have the shield under the limit switch part that sticks over the burner could the fan air be cooling too fast causing it to shut off?

  13. Is this adjustable without replacing the thermostat, if so how do you adjust it and where do you set it at?

Comments are closed.