Heat not working? What to check before you call

The first genuinely cold night of the year is when most people find out their heat is not working, and it is also the night every heating contractor in the county is already out. So before you get in that line: a surprising share of these calls end at a switch, a thermostat or a breaker, and you can check all of them in about ten minutes.

Work through this in order. If you get to the end and the heat is still not working, you will at least know what to tell whoever you call, which usually means the right part arrives on the first visit.

Heat not working everywhere, or just one room?

• One radiator cold, everything else fine. Not a fault with the boiler. That is the radiator or its valve, and the cold-radiator checks are in our guide to a boiler that is not working.
• One floor cold. Usually a zone — a zone valve or its thermostat, not the whole system.
• Nothing anywhere. Carry on down this list.

The thermostat, properly

More no-heat calls end here than anywhere else, and it is worth being systematic rather than glancing at it.

• Change the batteries even if the screen looks fine. A dying battery will run a display and still fail to close the circuit that fires the system.
• Check it says HEAT, not COOL or OFF. Easy to knock, and easy to miss on a flat touchscreen.
• Push the set point well above room temperature — five degrees, not one. Some units have a wide swing and will sit there doing nothing on a one-degree difference.
• If it is a smart thermostat, check it has not lost power or schedule. A C-wire problem shows up as a thermostat that works for days and then goes blank.
• Listen. Within a minute of pushing the temperature up you should hear something start somewhere. Silence tells you the signal is not reaching the unit; noise tells you it is and the fault is further on.

The switch almost nobody knows about

There is usually an ordinary-looking light switch at the top of the basement stairs, or on the wall beside the boiler or furnace itself, and it is the emergency shut-off for the heating. It gets turned off by someone looking for a light, by a contractor, or by a child, and then the heat is not working and nothing seems to be wrong.

Check it. Then check the breaker panel for a tripped breaker. Between those two and the thermostat batteries, that is the majority of the heat not working calls that could have been avoided.

Worth knowing before winter rather than during it: find that switch and the breaker now, while the house is warm and you are not reading this by flashlight.

When it is the boiler, not a setting

If the switch, the breaker and the thermostat are all fine and the boiler still will not fire, keeps locking out, or runs while the radiators stay cold, your heat is not working because of the boiler, not a setting. The pressure gauge, the reset button and cold radiators each tell you something different, and they are taken one at a time in our guide to a boiler that is not working. Two things to know first: press a reset button once, never over and over; and if the heat is not working and you have no hot water as well, that points at the boiler itself rather than at the heating side of it.

Banging and knocking on a one-pipe steam system is usually a vent or a pitch problem, not the boiler. Common in the older housing in Yonkers and the river villages, and fixable; what each kind of noise means is in our guide to banging pipes.

Stop and call instead if any of this is true

• You smell gas. Leave the building, then call the gas utility from outside. Not a heating job until they have made it safe.
• A carbon monoxide alarm has sounded. Out, then emergency services. Do not go back to investigate.
• There is water around the boiler, or a pressure relief valve is discharging.
• Soot, scorching or a smell of burning around the unit.
• It locks out every time you reset it. Twice is information. Ten times is a hazard.
• The house is dropping below about 55°F and it is forecast to freeze, because now you have a plumbing problem coming as well as a heating one.

Renting? If the landlord supplies the heat, getting it fixed is the landlord’s job, and some cities spell out how warm. In White Plains the city enforces the state rule that a landlord who supplies heat keeps habitable rooms at 68°F or more from September 15 to May 31, so the landlord or managing agent is the first call.

What to say when you call about heat not working

Four answers make the visit shorter and the fault much more likely to be fixed on the spot: whether it is the whole house or one room; whether you have a boiler or a furnace; whether there is hot water; and what the unit does when you push the thermostat up — nothing, fires and stops, or runs and produces nothing.

If the heat is not working and the checks above have not found it, the next step depends on what you have. KBD covers gas boilers, steam and hot-water heating — that is boiler repair, and cold radiators with a working boiler is usually radiator and valve work. If it is the middle of the night and the house is getting cold, it is an emergency call and the phone is answered.

Forced-air furnaces are not our trade. If that is what you have, the checks above are still worth doing, but the repair itself is a heating contractor’s job rather than ours — and we would rather tell you that now than after a visit.

KBD Plumbing & Heating covers gas boiler and radiator heating across lower Westchester — Dobbs Ferry, Hastings-on-Hudson, Irvington, Yonkers, White Plains and the rest. Licensed and insured, price agreed before work starts, nights, weekends and holidays included: (914) 233-3000.

More advice from the job