Furnace short cycling could be your thermostat

Furnace short cycling could be your thermostat. Here is a way you can tell along with some other causes. This could save you big big bucks as many of the common causes are easy fixes. If you have questions I am happy to try and help :)

[bert]

you could bypass the thermostat by using a jumper wire from the red thermostat terminal to the white terminal. if it doesn't short cycle it's the thermostat. if it does short cycle try cleaning your flame sensor

[zeuscarver]

I had the same exact 2 thermostat models as you. It was convenient to re-use the back plate. The only thing I don't like about the 3000 model (new) is the battery life. It starts flashing for low battery in less than 1 year whereas the 4000 model (old) batteries lasted for 3+ years. My 4000 model starting glitching around 10 years. Not great longevity. Also, the temperature on the thermostat will change just by handling it. The body heat from your hand will actually change the temperature and it can take several minutes to stabilize after putting it down.

[jungleviper]

After installing a smart thermostat my furnace starred short cycling

[DJRides]

I need to send you a case of beer or something. Been searching like crazy for a solution and unfortunately paid and had 3 different techs (all from the same company - my mistake) to try and diagnose and fix the issue (replaced aquastat and all zone valves) to no avail. Saw this video, went to home depot immediately and bought new thermostats. Thermostat in our den was not reading temp correctly. Replaced it and voila now the furnace works great with no short cycling. Ours would turn on and off rapidly, sometimes upwards of 5-10 times in a row.

[trampledunderfoot]

I know I'm late to comment, but I'd appreciate any thoughts and advice anyone might have. My furnace started short cycling about a week ago. Set at 69, it would run just until the point where the room temperature would reach 69 then immediately the thermostat screen would go blank, the furnace would blow cool air for a couple seconds, then shut off. The instant the furnace would shut off, the thermostat screen would come back on. The screen would read 69 for the set temperature and 73 for the room temperature. After about two seconds, the room temperature changes to 68, the furnace would kick back on blowing warm air until the temperature hit 69 again and the thermostat would go blank and it would all repeat.

I'd forgotten to change the furnace filters, and they were pretty dirty. I changed them, and it didn't help, the same thing would happen. I took the filters out, and the furnace and thermostat run normally no problem. I put one filter in, and it runs normally no problem. I put both filters in, and the problem starts up again.

A couple of months ago my thermostat started flashing the word "battery". At that time, it was news to me that thermostats needed batteries, opened mine up, and lo and behold there are batteries leaking acid. I took the old ones out, brushed off as much acid as I could, put new batteries in, and the thermostat worked fine.

I thought it was a sure sign it was the filters when it worked when the filters were out, but clean filters don't help. Could this be the thermostat? Or what? Thanks to anyone who has ideas.

[cloudchaser]

my thermostat drops one degree after 5 minutes and then my heat comes on again. been having this issue for the past 10 years.

[TrentG]

My 1984 boiler would turn on and run for a bit then turn off, and continue doing thst would.run for 30 seconds to a minute then turn off while never reaching targeted temp. Changed the old mercury thermostat to a cheap nest E and it now runs like it's supposed to, boiler stayed on until the temperature was met and maintsined heat.

[chrisitinabobinski]

Yep the next thing to check is zone valves .

[terrykobs]

it doesnt flash when its on a lower setting. can i replace the thermostst my self.thank you for the help.

[terrykobs]

i cani turn my furance higher then 70 degrees. then the lights on my furance starts flashing. what wtong??

[kim_]

My Thermostat reads 76 and says 76 inside but feels 79 in house its reading wrong I have the same brand as you and changed my filter what might be going on

[yeager]

Not sure this is short cycling, but my furnace turns on and runs for about 20-30 and then shuts off. Then, about 5-10 minutes later it turns on and runs for 15 minutes. It repeats this all the time and the house remain heated and comfortable. It doesn't turn on and off and on and off incessantly. We also have two identical (older) thermostats, centrally located, albeit one inch apart in the living room. Huh??? Any ideas?