Guide
Furnace running but no heat
You hear the fan and feel air at the vents, but it is cold. That narrows the problem a lot.
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First, is it the fan setting?
Many thermostats have a fan switch with on and auto. On on, the blower runs all the time, even when the burners are off, and the air feels cool. Set it to auto and wait a few minutes. If heat comes back with the next cycle, there was no fault at all.
If the fan is on auto and the air is still cold
The furnace is in lockout
After several failed lighting attempts, the control board stops trying and may keep the blower running to cool the heat exchanger. A flashing light on the board usually shows a code.
The filter is choked
With too little airflow, the heat exchanger overheats and a limit switch shuts the burners off while the fan keeps going.
The vent or drain is blocked
On a high-efficiency furnace, snow over the outside pipes or ice in the condensate drain stops the pressure switch from closing, so the burners never light.
The flame sensor is dirty
The burners light, run a few seconds and drop out, over and over.
No gas is reaching it
If the gas stove also will not light, the problem is upstream of the furnace. Call Avista, not an HVAC contractor.
The igniter failed
You hear the draft motor, then nothing lights, then the cycle repeats.
Safe checks to make
- Replace a dirty filter and turn the power off and on at the furnace switch to reset it.
- Go outside and clear snow and ice from the vent pipes, if your furnace has them.
- Look for water around the furnace. A pooled drain may point to a blocked trap.
- Write down the blink pattern of the board light before you reset anything.
If one reset does not hold, leave it off and call. Repeated resets can mask a safety problem.
When it is more than a nuisance
If the furnace shuts down because of venting, or if a CO alarm sounds, treat it as a safety issue. Leave the house, call 911, and follow the steps in the carbon monoxide guide. If you smell gas, Avista asks you to leave, avoid sparks and call 911 and then Avista at (800) 227-9187.
Source: Avista natural gas safety.
Where these facts come from
Cold house in Spokane? Talk to a contractor now.
Dial the number and explain what the heat or cooling is doing. The person who picks up runs an independent HVAC business working in Spokane and the towns nearby.