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Furnace Not Heating? Checklist Before You Call
Most no-heat calls end with a simple fix. Before booking a visit that costs $100-$200 just to diagnose the problem, run this checklist. It takes about ten minutes and resolves a large share of winter furnace trouble without a service fee.
Check these first
- Thermostat: set to heat, fresh batteries, and five degrees above room temperature so it actually calls.
- Breaker and furnace switch: the furnace has its own switch that looks like a light switch, often at the top of the basement stairs.
- Air filter: a clogged filter trips the high-limit switch and shuts the burner down.
- Gas valve and vents: confirm the valve is open and the exhaust and intake pipes are clear of snow, nests or leaves.
- Condensate drain: high-efficiency furnaces lock out when the trap fills with water.
Read the fault code first
Modern furnaces store the last fault. Open the blower door and watch the LED, then count the flashes: steady on means normal, and a repeating pattern is the code. A three-flash code usually points at the pressure switch, four at the high-limit or rollout, and five or six at the flame sensor or ignition. Write the number down before you call, because a technician can price the repair from it and you will not pay for diagnosis twice.
What each repair typically costs
| Item | Typical cost |
|---|---|
| Service call and diagnostic | $100-$200 |
| Ignitor or flame sensor | $150-$350 |
| Inducer motor | $400-$700 |
| Blower motor | $400-$800 |
| Control board | $500-$1,000 |
| Full furnace replacement | $3,500-$8,000 |
Thermostat problem or furnace problem?
If the thermostat screen is blank, it is a power problem: batteries, the C-wire, or the breaker. If the thermostat calls for heat and the blower runs but the air stays cold, the burner is not lighting, so suspect the ignitor, flame sensor or gas supply. If nothing runs at all, check the blower door, because the safety interlock only closes when the door is properly seated.
Safety: when to stop and call a pro
Smell gas? Leave the house and call the gas utility from outside, and do not flip switches on the way out. Never bypass a safety switch or limit to force heat, because carbon monoxide has no smell and no cheap sensor is a substitute for the real interlocks. If a technician finds a cracked heat exchanger, replacement is mandatory rather than optional.
Furnace age, efficiency and when to upgrade
Furnaces last fifteen to twenty years. Units installed before 2010 often run at 80 percent efficiency, while modern condensing models reach 96 percent by capturing heat from the exhaust. On a $900 annual gas bill, that gap is roughly $150 a year, so a $4,000 replacement pays back in a decade – unless the old unit is failing, in which case safety rather than savings drives the decision.
Why annual tune-ups matter
A $100-$200 annual service cleans the burners, checks the ignitor, verifies combustion and measures the temperature rise across the heat exchanger. Most winter no-heat calls trace back to a filter that was never changed or a sensor that was never cleaned. Change the filter monthly through heating season, which is the cheapest insurance a homeowner can buy.
How long repairs take
Ignitors and flame sensors are same-day jobs of one to two hours. Inducer and blower motors usually need a part ordered in, so plan for one to three days in cold weather and keep the thermostat low so the house does not lose all its heat. Control boards are often in stock and replaceable the same visit.
FAQ
- Why does my furnace short-cycle? Usually a clogged filter or a failing high-limit switch.
- How long do furnaces last? Fifteen to twenty years with annual service.
- Repair or replace? If a repair exceeds a third of replacement cost on a unit over fifteen years old, replace.
- Is a service plan worth it? Often yes, since tune-ups run $100-$200 and repairs are discounted.
Related reading: the 50% repair-or-replace rule and vetting a contractor.