The furnace will not run and the house is getting colder

Why it will not come back on its own

A gas furnace counts its own failed attempts. After three or four tries at ignition it locks out and stops trying, and it stays that way until the fault behind it is corrected.

Switching the breaker off and on resets the count, not the fault. The furnace lights once more, then locks out again an hour later — the same failure, one cycle further along.

Two things are worth ruling out first, because neither is a repair. A thermostat on dead batteries sends no call for heat, and the switch on the furnace door has to be closed for anything to run at all.

The house does not hold heat for long. Vineland, NJ sees about 108 nights a year below freezing, and a house here usually runs one gas furnace with nothing to fall back on.

What the visit involves

A technician follows the sequence in the order the furnace does: the call for heat, the inducer, the pressure switch, the ignitor, the flame signal at the sensor, then the limit. Each step either passes the job to the next or stops, and where it stops names the part.

A dirty flame sensor, a cracked ignitor and a pressure switch held open by a blocked flue all read the same from the hallway — nothing running — and they are three different repairs at the furnace.

What to say when you call

• That there is no heat in the house at all right now
• What the thermostat is set to and what it is reading, both numbers
• Roughly when the furnace was installed, and the brand off the data plate
• Your address and ZIP code, and where the furnace sits

Common questions

It ran fine yesterday. What changed overnight? Usually nothing did. A flame sensor coats slowly and an ignitor cracks under its own heat cycles; the night it finally fails is the night the furnace is asked to run longest.

Is it just the thermostat? Sometimes, and a set of batteries settles it in a minute. A lit display that still produces nothing at the furnace has already done its part.

Can a technician come out today? Call to check whether a same-day visit is available. That answer belongs to the day and to whoever is taking calls in your ZIP code.