A gas furnace has more safety interlocks than any other appliance in your house, and most no-heat calls are one of those interlocks doing its job correctly.
Know where to stop
Everything below is a check any homeowner can safely make. Anything involving opening a sealed refrigerant circuit, working inside an energized panel, or dismantling a gas train needs a licensed technician — not because we want the call, but because that is where people get hurt.
If you smell gas, leave the building and call the gas utility from outside.
Free things to try before you call
A good share of the calls we go out on turn out to be one of these. Try them first, and you may save yourself a service charge.
- 01
Check the thermostat is on HEAT with the setpoint above room temperature, and replace its batteries
- 02
Replace the air filter — a blocked one trips the high limit and shuts the furnace down
- 03
Check the furnace breaker, and the switch on or near the furnace that looks like a light switch
- 04
Make sure the furnace door panel is properly closed — a safety switch stops it running otherwise
- 05
Check the gas valve to the furnace is open, and that other gas appliances still work
- 06
For a condensing furnace, check the condensate drain is not blocked — a full trap shuts it off
- 07
Look outside for a blocked intake or exhaust vent pipe, especially after snow or a bird’s nest
- 08
Note any flashing error code on the control board through the sight glass — tell us the pattern
What it probably is
These are the most likely causes. Open one to see what it looks like and what fixing it involves.
1A dirty flame sensor
This one is very common and inexpensive to put right. The sensor confirms a flame is present; when it gets coated it stops seeing the flame, so the furnace lights, runs a few seconds, then shuts off for safety and tries again. Usually cleaning it fixes it entirely.
2Igniter failure
The furnace goes through its start sequence but never lights. Hot surface igniters are consumables and fail eventually, and replacing one is straightforward.
3Pressure switch or inducer motor
The inducer draws combustion gases through the heat exchanger, and the pressure switch confirms it is doing so. A failing inducer, or a blocked vent, stops the furnace before it will light.
4High limit tripping on airflow
The furnace starts, then shuts down after a minute or two. It is almost always airflow: a blocked filter, closed vents or a failing blower letting the heat exchanger overheat. Left alone it damages the heat exchanger, so it is worth fixing promptly.
5A cracked heat exchanger
This is the one we hope not to find. A crack lets combustion products, including carbon monoxide, into the air you breathe. It is not repairable — it means a new heat exchanger or a new furnace, and the system must stay off until then. If we find one, we will give you a clear answer.
Common follow-ups
My furnace starts then stops after a minute. Why?
Classic short-cycling on the high limit, and it is nearly always airflow rather than the burner. Change the filter and open all the vents. If it persists, the blower or the ductwork needs looking at.
What does the flashing light on my furnace mean?
It is a diagnostic code, and the legend is usually printed inside the furnace door. Count the flash pattern and tell us when you call — it often means we arrive with the right part already on the truck.
I smell gas. What do I do?
Leave the building. Do not switch anything on or off on your way out, including light switches. Call the gas utility from outside. Call us afterward, once they have made it safe.
Prefer to call?
(423) 357-1922- Office hours
- Monday to Friday, 8–5
- Outside those hours
- Emergency service is available — call the same number.
- Where we go
- Church Hill, Kingsport, Mount Carmel, Surgoinsville, Rogersville, Johnson City, Bristol, Greeneville, Morristown and across into Southwest Virginia. Full service area.
- Where we are
- 119 E Main St, Church Hill, TN 37642
Still not working after these checks?
That is what we are here for, and emergency service is available.
(423) 357-1922