Heating repair starts with knowing which system you have, because a gas furnace, heat pump, boiler and electric baseboard each fail in their own ways. A large share of no-heat problems turn out to be a thermostat setting, a tripped breaker or a clogged filter, so check those first. If the heat is out in freezing weather, protect people and pipes before anything else.
This guide sorts symptoms by system type and sends you to the detailed guide for your equipment.
Which Heating System Do You Have?
- Gas or propane furnace. A metal cabinet with ductwork, supply registers and a flue or PVC vent pipe. Heat comes from burners.
- Electric furnace or air handler with heat strips. Ducted like a gas furnace, but no gas line or flue. Heat comes from electric elements.
- Heat pump. An outdoor unit that runs in winter as well as summer, paired with an indoor air handler or furnace. It moves heat rather than making it.
- Boiler. Heats water and pumps it through radiators, baseboard convectors or radiant floor tubing. No ductwork for heat. Often called hot water heating or hydronic heat.
- Electric baseboard. Individual heaters along the walls, each with its own thermostat, usually wired at 240 volts. The baseboard heater guide covers thermostats, limit switches and sizing.
Many homes combine two. A heat pump with a gas furnace backup is a dual-fuel system, and a boiler home may use a mini-split for cooling. If you're weighing a different system type, the boiler vs furnace comparison lays out the trade-offs.
Heating Problems by System Type and Symptom
| System | Symptom | Common causes | Go deeper |
|---|---|---|---|
| Gas furnace | No heat, nothing runs | Thermostat, breaker, service switch, furnace door switch, blown board fuse | Gas furnace repair guide |
| Gas furnace | Lights, then shuts off | Dirty flame sensor, pressure switch, limit switch tripping on a clogged filter | Furnace not working checklist |
| Gas furnace | Blows cold air | Ignition lockout, fan set to On, gas supply off | Furnace blowing cold air |
| Heat pump | Outdoor unit iced solid | Failed defrost control or sensor, low refrigerant, outdoor fan problem | Heat pump repair |
| Heat pump | Air feels lukewarm, runs constantly | Normal in very cold weather, or low refrigerant, dirty coil, reversing valve | heat pump repairs |
| Heat pump | "Aux" or "Emergency Heat" always on | Outdoor unit not running, tripped outdoor breaker, thermostat setup | Heat pump repair |
| Boiler | Radiators cold, boiler hot | Stopped circulator pump, closed zone valve, air in the system | Boiler repair guide |
| Boiler | Pressure low or relief valve dripping | Leak, failed expansion tank, fill valve problem | Boiler repair guide |
| Electric furnace | Fan runs, air stays cool | Tripped heat-strip breaker, failed sequencer or element | Tech diagnosis |
| Electric baseboard | One room cold | Wall thermostat, breaker, failed element, furniture blocking airflow | Tech or electrician |
| Any system | CO alarm, gas smell, burning smell | Combustion, venting or electrical fault | Leave the house, call from outside |
No Heat in a Freeze: Stay Safe While You Wait
When the heat goes out in severe cold, safety comes before the repair.
Carbon monoxide. Keep CO alarms working on every level and near bedrooms. Never heat the house with a gas oven or range, a charcoal or gas grill, a camp heater, or a generator. Run a generator outdoors, well away from doors, windows and vents, never in a garage, even with the door open. If a CO alarm sounds, get everyone outside and call 911.
Temporary heat. An electric space heater with tip-over and overheat shutoff is the safest stopgap. Plug it directly into a wall outlet, not an extension cord or power strip, keep 3 feet of clearance, and turn it off when you sleep or leave the room. Don't use unvented kerosene or propane heaters indoors.
Frozen pipes. Let faucets on exterior walls drip, open sink cabinet doors so house air reaches the pipes, and close off unused rooms to concentrate heat. Know where the main water shutoff is. If a pipe freezes, thaw it with a hair dryer working back from the faucet, never with an open flame or torch. If a pipe bursts, shut off the main water right away.
Boiler homes. Hydronic piping in exterior walls and baseboard can freeze too. If the boiler is out for a long stretch in a hard freeze, tell the technician, because a frozen heating loop can crack.
Propane. If your propane tank ran empty, don't relight pilots or appliances yourself after the delivery. (For a pilot that went out for another reason, see how to relight a furnace pilot light.) Suppliers commonly perform a leak check before restoring service, and many jurisdictions require one. The propane furnace guide explains why that leak check matters.
What You Can Safely Check Before Calling Anyone
Start with the checks that apply to every system:
- Thermostat. Set to Heat, setpoint above room temperature, fresh batteries. On a heat pump, set it to Heat, not Emergency Heat.
- Breakers. Furnaces, air handlers, heat pumps and boilers each have their own breaker, and electric heat often uses two or more. Reset a tripped breaker once. If it trips again, leave it off.
- Switches. Look for a service switch beside a furnace or a boiler's emergency switch, often a red plate at the top of the basement stairs.
- Filter. A clogged filter starves a furnace or heat pump of airflow.
- Fuel. Check the propane or oil tank gauge and that other gas appliances work.
Then system-specific checks:
- Furnace: confirm the blower door is seated, read the LED flash code, and clear snow from PVC vent pipes.
- Heat pump: clear snow and ice buildup around the outdoor unit. Steam and a stopped outdoor fan for a few minutes is a normal defrost cycle.
- Boiler: read the pressure gauge and compare it to the label, and look for leaks around the boiler and radiators.
What Not to Touch
Never bypass a limit, rollout or pressure switch, open a gas valve or burner assembly, or chip ice off a heat pump coil with a tool. Don't open the refrigerant circuit, which requires EPA Section 608 certification. Leave capacitors and wiring alone, since capacitors hold a charge with the power off. If you smell gas, leave the house and call the gas utility from outside.
What a Heating Repair Involves
A good diagnosis follows the system's sequence and measures before replacing anything. The details depend on the equipment:
- Gas furnace: read the board's flash code, then check the inducer, pressure switch, ignitor, gas valve and flame sensor in order. The gas furnace repair guide walks that sequence part by part.
- Heat pump: check refrigerant pressures and temperatures, the defrost board and sensor, the reversing valve, the outdoor fan, the capacitor and the auxiliary heat strips. See heat pump troubleshooting and repair.
- Boiler: check pressure, the circulator, zone valves, the expansion tank, ignition and the low-water cutoff. The boiler repair guide covers each.
- Electric furnace and baseboard: measure voltage and resistance at the elements, sequencers, limits and thermostats.
For combustion equipment, the technician should also check venting and carbon monoxide before leaving.
What Affects Heating Repair Cost
The failed part sets most of the bill:
- Low end: thermostat fixes, flame sensor cleaning, capacitors, clearing a condensate drain.
- Middle: ignitors, pressure switches, sequencers, heat strips, zone valve motors, circulator pumps.
- High end: control boards, blower and inducer motors, expansion tanks with system draining.
- Top: a furnace heat exchanger, a heat pump compressor or a leaking boiler heat exchanger, often enough to justify replacement.
Other factors: system type and efficiency tier, OEM-only parts, parts warranty status, attic or crawlspace access, and after-hours rates during a cold snap. For the replacement side, see the furnace replacement prices and heat pump pricing guides.
Should You Repair or Replace Your Heating System?
Typical lifespans give you a baseline: gas furnaces and boilers often last 15 to 30 years, and heat pumps around 15 to 20. The 50 percent rule is a useful starting point. If a repair costs more than half the price of new equipment and the system is past the middle of its life, replacement usually makes more sense.
Replace sooner when a heat exchanger cracks, a heat pump compressor fails out of warranty, parts are discontinued, or you're facing repeat breakdowns. When you replace, it's also the moment to reconsider system type. The whole-system HVAC repair guide covers replacing heating and cooling together.
How to Vet a Heating Repair Contractor
Pick a contractor who works on your system type every week. Plenty of companies are strong on furnaces and AC but rarely touch boilers, oil burners or cold-climate heat pumps.
Questions to ask:
- How often do you service this type of system and this brand?
- What did you measure to confirm the failed part?
- Will you check for carbon monoxide and venting problems on combustion equipment?
- Is the part covered by a manufacturer warranty, and what labor warranty do you give?
- Does the diagnostic fee apply to the repair?
Red flags: pushing a full replacement before diagnosing, condemning a heat exchanger without showing evidence, quoting refrigerant top-offs without finding the leak, and offering to bypass a safety control to restore heat.
Frequently Asked Questions
Why is my heater running but not heating the house?
On a furnace, the burner has usually locked out while the fan keeps running, or the thermostat fan is set to On. On a heat pump, look for a frozen outdoor coil, a defrost cycle, or a refrigerant problem. On a boiler, low pressure, air in the lines or a stopped circulator pump are the usual causes.
What should I do if my heat goes out in winter?
Check the thermostat, breakers and filter, then the system-specific basics like the furnace door, boiler pressure or heat pump disconnect. If that doesn't restore heat, keep people warm with safe electric space heaters, protect pipes by letting faucets drip and opening sink cabinets, and keep CO alarms working. Never heat the house with an oven, grill or unvented heater.
How long can a house go without heat before pipes freeze?
It depends on outdoor temperature, insulation and where the pipes run. A well-insulated house can hold heat for a day or more in moderate cold, but pipes in exterior walls, crawlspaces and garages can freeze within hours in a hard freeze. A common rule of thumb is that pipes are at risk once outdoor temperatures fall to about 20 F.
Is it safe to use a space heater when the heat is out?
An electric space heater with tip-over and overheat protection is the safest temporary option. Plug it directly into a wall outlet, keep it 3 feet from anything that can burn, and turn it off when you sleep or leave the room. Don't use fuel-burning heaters indoors unless they're designed and vented for indoor use.
Should I repair or replace my heating system?
Repair when the system is mid-life and the fix is a single part. Get a replacement quote when the repair is more than half the cost of new equipment, the system is near the end of its typical lifespan, or a major part like a heat exchanger or compressor has failed.
Before you hire anyone, run through the contractor questions above so the visit starts with a real diagnosis.