You can fix this
Likely cause: a thermostat setting
If the thermostat was off, on Cool, or set below the room temperature, the furnace had no reason to run. Fixing the setting brings the heat back.
Why this happens
Trane puts this first: make sure the thermostat is set to Heat and the room is colder than the temperature you set. Honeywell says that if the thermostat is in Off mode, or the set temperature isn't calling for heat, the system won't start. Carrier and Family Handyman list the same check first.
How to fix it
- Make sure the mode is on Heat and the set temperature is a few degrees above the room temperature.
- If you use a schedule, Family Handyman suggests checking that the thermostat shows the right day and time. It notes that a power outage with a dead battery can reset the thermostat to its default program.
- If the thermostat runs on batteries, Trane suggests replacing them and not ignoring a low battery warning.
- Give the system a few minutes before you change the setting again. Honeywell says changing it over and over during a built-in delay makes troubleshooting harder.
When to stop. If the heat stops again with the right setting, work through this guide again. If you notice a burning plastic or electrical smell once the furnace runs, Carrier says to turn the furnace off and have a qualified HVAC professional inspect it before you use it again. If you smell gas or rotten eggs, leave the house without touching any switch and call 911 or your gas utility from outside. If a carbon monoxide alarm sounds, or anyone feels dizzy, sick or has a headache, get everyone outside to fresh air and call 911. If you see smoke or flames, get out and call 911.
If this does not fix it, tell the HVAC technician
- What the thermostat was set to when the heat stopped.
- Whether the heat came on once the setting was fixed.
- Whether the setting keeps changing on its own.
- The thermostat brand and model.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
FourHome is our sister brand. Browse all FourHome replacement faucet and shower parts on the FourHome Amazon store. We earn from purchases made through this link.