[J1CS]

I noticed this weekend furnace will come on , then the flame starts and then blower for the house starts. After a few minutes flame goes out fan still is on because the thermostat in house has not been satisfied, flame comes back on, and then it happens again. So this takes place three times before the thermostat is satisfied, flame on then off, on then off, on then off, and the it cools down and shuts off,until the thermostat requests heat again. The furnace is a comfortmaster, 100,000btu for a 1500sq ft house. It was in house when we bought it in april. The furnace is around a 2000 model. Had a teck come out he thought furnace was too big for house, so he set the fan for high speed, heat and air cond. Also checked the a switch that was in the fir box, I think a switch that sinces heat in the box. He said that it was alright. He thought furnace was to big for house, and getting to hot in fire box cycling off and then on again. After setting high fan it only cycled two time instead of three times. So I was looking for another opion. Any more info needed, let me know. Sorry for lenth.

 

[Glasshousebltr]

Does it go off before or after it comes on?:cheesygri

Bob

 

[NickTech]

It sounds like your furnace is going off on hi limit. This is when the temp. of the furnace exceeds its design temp. many factors can contribute to this. An over sized furnace, undersized duct, not enough air volume moving across heat exchanger. Have someone check the manifold gas pressure, this is the pressure after the gas valve. it should be 3.5 " of H2O column. it is possible that the burner is over firing its rated BTU input. if pressure is proper then a burner port orfice can be changed. Have the tech check across the hi limit(s) terminals to see if in fact this is the case. Any good tech worth his weight should be able to fiqure this one out. :Thumbs:

 

[Comfortman]

how old is the house?
more importantly how old is the evaporator on top of it?
if the evaporator is plugged wih dirt that will over heat a furnace fast!

 

[J1CS]

A teck came out and checked things. Furnace might be a little large for the house 100,000 furnace a 1500sq ft house. Older duckwork straight run 14w about 30 35 ft long, with 10 outlets. Changed fan motor to run hight for heat as well as cool. Now it cycles on and stays on until the thermostat is satisfied. The unit is about a 2000 install. We moved in in april 04. Evaporator is on botton, will check that a little later.