Furnace primary blower

[Richardson]

I have a Trane 60,000 BTU updraft furnace, about three years old. Yesterday when the induction fan started up in response to the thermostat, it ran for about 5 seconds, then shut down. It has continued this pattern, although if I override the set temp on the thermostat and wait about a minute, it fires up normally and continues through the complete heating cycle. Could it be the thermostat?

[Marc]

How did you do this override?

Marc

[Richardson]

The override was done by rotating the temperature adjusting wheel on the thermostat.

[Richardson]

I should add that this is a programmable thermostat purchased 3 years ago at Home Depot.

[Nolan Kienitz]

Maybe change the battery in the T-stat.

[Brandon Whitmore]

I wonder if your rotary t-stat has a heat anticipator setting? If so, I'd replace it--it's not intended for your newer furnace, and it's probably not set correctly.

Pull the t-stat from the wall and connect the R & W wires-- I'll bet the furnace runs perfectly without the thermostat. If so, then yes, it's your thermostat.

[Richardson]

The thermostat is not the old round style, it is programmable. The wheel I mentioned is on the left side and allows overriding the set temp, among other functions.

Batteries are ok, I suspect air is the problem. The furnace sat all summer and now that cooler weather has arrived, this problem has surfaced. It's sporadic. Most of the time it starts up fine. This morning I heard the induction motor star, run for about 5 seconds, shut down, then immediately start up again.

I get the proper red flashes, fast red when calling for heart, slow red when not.

Assuming it is air in the line how do I bleed it?

[Brandon Whitmore]

It isn't air in the line. If the burner has fired and run recently, any small amount of air/stale gas would have bled quickly. Even if there was air in the line, the furnace would have made multiple attempts to fire and would have fired fairly quickly. (assuming natural gas here).

The status indicator lights will only flash a fault code right after there's an issue-- you likely know this, but just in case....

Start with the basics. Pull the thermostat from the wall, tie together R & W, and see if it runs properly for an extended period of time. If the burner ends up shutting off, and the blower runs for a while (cooling things down) before the burner re-fires, you've got an airflow/ over-heating issue. If it runs fine, you've got a t-stat issue. In order to eliminate the t-stat and wires, I always jump the furnace at the board.

[plummen]

I wonder if your rotary t-stat has a heat anticipator setting? If so, I'd replace it--it's not intended for your newer furnace, and it's probably not set correctly.

Pull the t-stat from the wall and connect the R & W wires-- I'll bet the furnace runs perfectly without the thermostat. If so, then yes, it's your thermostat.

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