fan comes on, occasionally no heat. - http://www.hvacmechanic.com/ Forums

Original message

mikeinpdx

71.117.201.121

"fan comes on, occasionally no heat." , posted Wed 21 May 11:48

I have a Tempstar gas furnace, not sure on the model number, but installed around 1999. Occasionally, the fan will come on, but no heat, even though the thermostat is showing the heat should be on. The fan will continue to run until I switch the thermostat off, then back on. Then I hear the burners ignite, the fan starts, and the furnace runs normally.

I've had the furnace inspected, the tech didn't see any problems. He didn't like the Lux thermostat and thought the thermostat was the problem.

I called Lux, they said if I remove the thermostat front plate when this happened, and the fan continued to run, it wasn't a thermostat problem, it was a furnace limit switch problem.

So the next time this happened (thermostat called for heat, fan went on, burners didn't ignite) I pulled the thermostat face plate and saw that the fan continued to run.

So how can I tell if this is a thermostat or furnace issue? Just replace the thermostat and see what happens? I've seen that Lux doesn't exactly have a good reputation on the various forums. What I liked about the Lux thermostat was that it has a mode where you can program the fan to run a certain number of minutes per hour, which keeps the house a lot more comfortable. In case this fan mode was causing the problem, I switched it to normal mode (where the fan only runs when heat or A/C is on) and I still see the same problem (no heat, fan running continuously). This happens maybe 1-2x per week.

Replies:

theduke03

24.250.18.179

"Re(1):fan comes on, occasionally no heat." , posted Wed 21 May 18:32

I'm sure your new stat and the old one are just fine. Could be a million things. You would need a meter to pinpoint the problem. Try cleaning your flame sensor with steel wool or a wirebrush. Flame sensor located in burner compartment:

"My dad was the most feared furnace fighter in Northern Indiana."

mikeinpdx

71.117.201.121

"Re(2):fan comes on, occasionally no heat." , posted Wed 21 May 19:32

Thanks! I'll check that out.

I thought it seemed odd that when this happened (fan on, no heat), I could disconnect the thermostat and the fan kept running. Made me wonder if it really was the thermostat causing the problem if I could do that.