Heating Repair & Diagnostics

Common Reasons a Furnace or Heat Pump Stops Working

When heat won't turn on, the cause often traces back to a handful of common culprits. A dirty flame sensor can prevent a gas furnace from staying lit, a failed igniter can stop ignition altogether, and a clogged air filter can restrict airflow enough to trigger a safety shutoff. Thermostat settings, dead batteries, or a tripped breaker are also worth checking before assuming the worst, since these simple issues account for a surprising number of no-heat calls. For heat pumps, a frozen outdoor coil, low refrigerant, or a failed reversing valve can all prevent the system from producing warm air even though the unit appears to be running.

Unusual noises can also point to specific problems. A loud bang at startup may indicate delayed ignition from a dirty burner, while a persistent clicking sound could mean a failing relay or control board. Short cycling, where the system turns on and off repeatedly, often points to a dirty filter, an oversized unit, or a faulty limit switch. None of these symptoms confirm the exact cause on their own, which is why a hands-on diagnostic is important before parts are replaced.

Safe Steps Homeowners Can Take First

Before calling for service, it's reasonable to check that the thermostat is set to heat mode and has working batteries, confirm that the circuit breaker for the furnace hasn't tripped, and replace the air filter if it looks dirty or hasn't been changed in the last one to three months. Do not keep resetting a breaker that trips again. Leave the equipment off and report what happened, since repeated tripping needs an electrical diagnosis.

What homeowners should avoid is opening up the furnace cabinet, working around the gas valve, or attempting electrical repairs without training, since furnaces involve combustion, electrical current, and sometimes natural gas or propane lines. If you smell gas at any point, leave the home and call your gas utility or 911 before doing anything else. A technician's diagnostic process typically involves checking the thermostat call for heat, verifying power and gas supply, inspecting the ignition sequence, and testing safety switches to isolate the actual fault rather than guessing at a repair.

An Iron Horse repair visit begins with a $120 diagnostic, waived when you go ahead with the repair. You see the repair price in writing before work starts. In Arizona homes with heat pumps, heating trouble can involve the same outdoor equipment used all summer, so note any cooling problems you noticed earlier in the year.