Check that this guide fits your situation.
Use this guide when
No heat or weak heat without a gas odor, carbon monoxide alarm, smoke or electrical warning sign.
Do not use it for
Opening a furnace cabinet, relighting burners, bypassing safety switches or working with gas and electrical components.
Stop and get help if
- A carbon monoxide alarm sounds or someone has possible exposure symptoms.
- You smell gas or notice smoke, sparking or a burning smell.
- The system repeatedly shuts off or trips a breaker.
Supplies
- Thermostat and equipment manual
- A matching filter if the user-accessible one needs replacement
Take it one step at a time.
- 01
Screen for an emergency
If a CO alarm sounds or gas is suspected, leave the building and call emergency services or the gas utility from outside. Do not keep troubleshooting.
Why this mattersFuel-burning equipment can present a serious safety hazard. - 02
Check the thermostat
Confirm Heat mode and a target above the current room temperature. If the thermostat uses replaceable batteries, follow its manual for a battery warning.
Why this mattersA setting or power issue can prevent a normal heat call. - 03
Check an accessible filter
Turn the system off. If a user-accessible filter is clogged, replace it with the correct size and direction per the equipment instructions.
Why this mattersA dirty filter can reduce airflow and affect system operation. - 04
Check visible airflow paths
Make sure room supply and return grilles are not covered by furniture or stored items. Do not open equipment panels.
Why this mattersAirflow restrictions can reduce comfort and may affect the system. - 05
Observe one normal cycle
Set the system back to Heat and give it time to start. Note whether the fan runs, whether air becomes warm and any displayed error code.
Why this mattersThe sequence gives useful information without altering internal components. - 06
Call if heat does not return
Share the equipment type, thermostat behavior, filter condition and any error code. Keep the system off if there are safety warning signs.
Why this mattersA technician can evaluate combustion, controls or electrical faults with appropriate tools.
No → check thermostat and user-accessible filter, then observe one cycle.
Yes → leave the area and contact emergency help from outside.
Check the result.
If it improved
Monitor the next cycle and keep a working CO alarm where applicable.
If it did not
Call for heating service and describe the system behavior and any error code.
Source guidance
These public resources informed the safety boundaries and general steps. The exact equipment and conditions at your property may differ.