Furnace Repair

A furnace that starts, runs for a minute or two, then shuts off and repeats is almost always a flame-sensing or airflow problem — a dirty flame sensor that can no longer prove flame, or a clogged filter tripping the high limit. A furnace that clicks and hums but never ignites points at the igniter or the pressure switch. A furnace that does nothing at all is usually electrical: a tripped breaker, a blown low-voltage fuse on the control board, a door switch left open, or a failed transformer.

Smells and sounds narrow it further. A brief dusty burn-off odor on the first run of the season is normal and clears in ten minutes. A persistent hot-metal or acrid smell is not — shut the system off. A rhythmic scraping or a loud rumble at startup is a blower wheel or a delayed ignition, and delayed ignition is worth treating as urgent because it means gas is accumulating before the burner lights.

Write down what you observed before you call. Whether the failure is intermittent or total, whether it started after a filter change or a power outage, and whether the thermostat screen is lit all change what we bring in the truck and often shorten the visit.

The visit starts with the thermostat and the filter, because both cause no-heat calls that need no parts at all. From there we watch a full ignition sequence and check the signals in order: call for heat, inducer start, pressure switch closure, igniter warm-up, gas valve open, flame proof, blower start. Whichever step the sequence dies on tells us where to measure instead of where to guess.

We test igniter resistance rather than replacing on suspicion, read flame-sensor output in microamps, verify pressure-switch operation against the actual inducer draft, check manifold gas pressure, and measure blower amp draw against the nameplate. On any gas furnace where combustion looks suspect, we inspect the heat exchanger visually and back it up with a combustion analyzer reading.

You get the findings before the quote: what failed, what the measurement was, what the part costs, and what happens if you wait. If a repair does not make sense on a system's age and condition, we say so and give you the replacement numbers alongside the repair numbers so you can compare them yourself.

Hot surface igniter replacement is the single most common furnace repair we perform. These silicon nitride and carbide elements are brittle, cycle to well over 1,800°F, and fail suddenly with no warning. Flame sensor cleaning is a close second — a light oxide film is all it takes for the board to stop proving flame and lock the unit out on a repeating short-cycle.

After those come pressure switches and blocked condensate or drain traps on high-efficiency units, inducer motors and their bearings, limit switch trips caused by a filter nobody changed, blower motor and capacitor failures, control board relay failures, and gas valve replacements. Ductwork restrictions and closed registers cause a surprising number of limit trips that get misread as furnace failures.

Heat exchanger cracks are the repair nobody wants. They are a carbon-monoxide risk, they cannot be safely patched, and the honest answer on a fifteen-year-old furnace is usually replacement rather than a heat exchanger swap. When we find one, we document it with photos, red-tag the unit, and walk you through both paths without pressure.

Valley furnaces run perhaps 200 to 400 hours a year, where a Midwest furnace runs several thousand. Low runtime sounds protective, but it creates its own failure pattern: dust settles on burners and sensors during the long summer, spider webs and insects block pressure-switch tubing, rodents nest inside attic and closet air handlers, and rubber and plastic components bake in a 140°F attic all summer without ever being exercised.

The other Arizona-specific factor is that most of our heat lives inside a package unit or a gas-pack on the roof, or in an attic air handler paired with a cooling coil. Both locations mean the furnace shares a blower and a duct system with a cooling season that beat on it for five months. Airflow problems created in July show up as heating faults in December.

That is why the first cold snap produces a flood of calls each year and why a fall inspection catches most of it. If your heat has not run since March, the cheapest thing you can do is turn it on for fifteen minutes on a mild day in October and find out now instead of at 6 a.m. on a 34°F morning.