Just great. It’s cold as penguin’s beak outside and now your furnace is blowing cold air (sometimes intermittently) out the air vents.
Why is this happening?
There are a few causes of this issue.
1) The thermostat fan is set to “ON”
“ON” means the furnace’s blower is running constantly—whether the furnace is heating it or not.
Simple fix: Turn the fan setting to AUTO. Now only heated air will come out the vents.
2) Dirty air filter is causing furnace to overheat
A dirty air filter decreases airflow to the heat exchanger (the part that heats the air), causing it to overheat. If it overheats, a limit switch shuts down the furnace burner (the part heating the heat exchanger).
Basically, your furnace is trying not to kill itself.
Simple fix: Check the air filter. If it’s dirty, change it. Here’s how to change the filter.
3) Pilot light’s flame is out
Note: Only read this section if you have an older furnace with a pilot light.
When the pilot light goes out, the gas valve shuts, preventing the burners from igniting.
Simple fix: Try relighting the pilot light (instructions should be on your furnace door.)
If the pilot light goes out after a minute, something is wrong. Issues could include:
- Dirty pilot light
- Dirty/damaged thermocouple (the copper rod that senses if the pilot flame is lit)
- Flame isn’t reaching thermocouple properly
Call an HVAC contractor to find the problem if the pilot light does not stay lit.
4) Issues with draining condensate
Note: Only read this section if you have a high efficiency furnace (90%+ AFUE)
To work properly, a high efficiency furnace has to drain condensate out of the home through a drain.
If there’s an issue draining this condensate, a float limit switch will prevent the furnace burners from igniting to prevent any more condensate from forming.
A few issues with draining the condensate include:
- Clogged condensate piping
- Clogged condensate drain
- Issues with the condensate pump
Simple fix: Call an HVAC contractor to find the issue and fix it.
Pippin Brothers is the Lawton-area’s most trusted heating, air conditioning and plumbing company. We’ve been serving Oklahoma since 1978. Contact us for more information.