24/7 Furnace Repair on Long Island

• Tries to start but never lights: a cracked ignitor on gas; a clogged nozzle, fouled filter or electrodes on oil.
• Lights, then shuts off in seconds: usually a dirty flame sensor, one of the least expensive repairs there is.
• Hums or rattles, then nothing: a draft inducer motor seized after sitting idle all summer.
• Pressure switch code: the switch, its hose, a blocked flue or a plugged condensate trap on a high-efficiency furnace.
• Cycles off on high limit: restricted airflow from a clogged filter, closed registers or undersized returns.
• Soot, a smoky smell or a delayed whoosh on oil: treat it as urgent and call.

Tell us whether the furnace tries to start, whether the blower runs and what the status light is flashing. That decides which parts go on the van, so more repairs are finished on the first visit. If you smell gas or a carbon monoxide alarm goes off, leave the house and call 911 or the gas utility from outside first.

No-heat calls of every kind in the same records, 91 of them, had a median of $461. A flame sensor or ignitor costs far less than a control board or blower motor. See Long Island HVAC data for how these figures were collected.

• Gas: cracked ignitors, dirty flame sensors, inducer motors that stick after the summer, pressure switches tripped by a blocked vent or a plugged condensate trap, and control boards.
• Oil: clogged nozzles and oil filters, electrodes that need setting, a failing cad cell or primary control, and soot. An oil furnace that smokes, smells or starts with a delayed whoosh needs a combustion check, not another reset.
• Both: blower motors and their capacitors, and furnaces that overheat and shut off on the high-limit switch because the filter or returns cannot pass enough air.

On oil, press the reset once at most. Repeated resets can flood the chamber and cause a puff-back that spreads soot through the house.

We see this most in older homes where forced air was a retrofit, and in split levels and capes where the upstairs rooms sit at the end of a long duct run. A furnace in an attic adds its own risks: a blocked condensate drain can overflow onto the ceiling below. On these calls we check the filter location, the return air and the duct runs, not only the furnace itself, because a new part on a furnace that is starved of air will fail again.

1. On the phone. We ask whether the furnace tries to start, whether the blower runs and what the status light flashes, so the likely parts come on the van.
2. Safety checks. Gas leaks, carbon monoxide, flue draft and a look at the heat exchanger.
3. Diagnosis. Thermostat, power, filter, ignition sequence, flame sensor, pressure and limit switches, inducer and blower motors.
4. Price before work. You hear the cause, the fix and the price, and decide.
5. Repair and test. Full heating cycles, temperature rise across the furnace and heat at the registers before we leave.

Before you call, these pages cover the safe checks: no heat, furnace blowing cold air, boiler not firing and AC not cooling.

As an estimate for planning, the furnace and boiler replacement cost guide puts replacing a gas furnace at $3,500 to $8,500. See furnace replacement for gas, oil to gas and heat pump options. A recent example of a repair that saved the furnace: a noisy furnace in Commack, fixed by tightening a vibrating draft motor and resealing the flue.