Short answer: Start with the simple things Trane lists: thermostat set to Heat and above room temperature (with fresh batteries), the furnace power switch on, the breaker not tripped, and a clean filter. On newer furnaces with electronic ignition, a failed igniter or a control board fault needs a technician. If you smell rotten eggs, leave the house and call your gas company.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| Thermostat blank or not calling for heat | Dead batteries or wrong setting | Set Heat, raise setpoint, replace batteries | If it still does nothing |
| No sound at all from the furnace | Power switch off or breaker tripped | Check the switch near the furnace and the panel | If the breaker trips again |
| Furnace starts, then shuts off | Dirty filter (overheating) or flame sensor | Replace the filter | Yes, if it continues |
| Blinking light on the furnace | Error code from the control board | Read the code chart inside the panel door | Usually |
| Gas smell | Possible gas leak | Leave the house now | Call the gas company |
Safety first
If you smell rotten eggs, Trane advises leaving the house and calling your gas company. Do not operate light switches or try repairs until the danger has passed.
Homeowner checks
- Thermostat: set to Heat, a few degrees above room temperature. Replace batteries; check for an error message.
- Power switch: look for a light-switch-style switch on or near the furnace. Make sure it is on.
- Breaker: reset a tripped furnace breaker once. If it trips again, there is an electrical problem; call an HVAC company.
- Filter: replace a dirty filter, and make sure vents and returns are not blocked.
- Panel door: many furnaces will not run if the front panel is not fully closed.
Ignition problems
On newer furnaces with electronic ignition, Trane recommends calling a technician, who will check the control board for error codes. On older furnaces with a standing pilot, you can relight the pilot by following the instructions on the unit; if it will not stay lit, call a professional.
When to call a professional
- The furnace still will not start after these checks.
- The breaker trips again after one reset.
- The pilot will not stay lit, or the igniter does not glow.
- There is any gas smell or a blinking error code you cannot clear.
What it usually costs
HomeGuide (2026) puts most furnace repairs at about $125 to $480. Typical prices: flame sensor $80 to $250, igniter $100 to $250, control board $300 to $650, blower motor $300 to $900, draft inducer motor $400 to $1,100. Technicians charge about $75 to $150 per hour, more for emergency service.
Frequently asked questions
Why won’t my furnace kick on when the thermostat calls for heat?
Common reasons are a power switch turned off, a tripped breaker, an overheating shutdown from a dirty filter, or an ignition problem.
Is there a reset button on a furnace?
Some furnaces have one, but repeated resets can hide a real problem. Turning power off and on at the switch is the usual reset; if it keeps failing, call a technician.
My heater is not working at all. Where do I start?
Work through the same order: thermostat (Heat mode, setpoint, batteries), the furnace power switch, the breaker, the filter and the front panel door. Most “heater not working” calls end at one of those.
Related problems
- Furnace blowing cold air
- Heat pump blowing cold air
- Breaker keeps tripping
- No hot water
- Thermostat not working
Sources
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.