You set the thermostat to 70 for the night, hear the familiar thump of the burner, and then the furnace shuts off again two minutes later. Or the blower runs and runs and the house never warms up. How a forced air system misbehaves is the first clue, so pay attention to it before you pick up the phone.
All Island Comfort, which services furnaces in both counties from Wading River, says natural gas is the most common new installation where there is a gas main on the street, and oil is common where there is not. Know which fuel yours burns before you call.
The furnace problems Long Island techs see most
All Island Comfort publishes the list of furnace problems it is called for most. If you can tell the company which of these you are seeing, the technician arrives with a better idea of what to bring.
- no heat, or the furnace will not turn on
- blowing cold air
- short cycling, or running constantly
- ignitor or pilot failure, a tripped flame sensor, a failed gas valve
- a clogged condensate drain on a high-efficiency unit
- a cracked heat exchanger
- a failed blower or inducer motor, or a bad capacitor
- limit switch lockouts
- noises, thermostat faults, dirty filters and high bills
Write down when it happens, too. A furnace that quits after ten minutes every time tells a different story than one that will not start at all.
How oil furnaces and gas furnaces differ on a service call
An oil furnace is really two machines: the furnace cabinet with its blower and heat exchanger, and the oil burner bolted to the front. When an oil furnace stops, the burner is the usual suspect. All Island Comfort’s yearly burner service replaces the nozzle and oil filter, cleans the pump strainer and runs a combustion test, and Beckett’s manual says a qualified technician must service its burners annually. If your oil furnace has skipped that visit, start with oil burner service.
A gas furnace has no nozzle or oil filter. Its weak points are on the ignition side, the ignitor, flame sensor and gas valve, plus the condensate drain on high-efficiency models. If you smell gas, do not touch the thermostat or any switch. National Grid’s Long Island instruction is to go outside and call 1-800-490-0045 or 911.
Furnace filter schedule
Dirty filters are on All Island Comfort’s furnace problem list. Their replacement schedule:
- standard 1-inch fiberglass filters: every 30 to 60 days in heating season
- 4 or 5-inch pleated filters: every 6 to 12 months
Write the date on the edge of the filter when you put it in, so you are not guessing at the next change.
The cracked heat exchanger conversation
The heat exchanger is the wall between the flame and the air you breathe. All Island Comfort calls a crack a serious safety concern and a reason to replace the unit, and lists it among the common sources of carbon monoxide along with a blocked flue. The Department of Energy warns that combustion gases leaking into the house can cause carbon monoxide poisoning, and suggests every home have a working CO alarm.
Because a cracked heat exchanger usually means a new furnace, it is also the diagnosis to be most careful about. If a technician tells you yours is cracked, ask to see it, ask for a photo, and ask what the combustion test showed. Getting a second opinion before you replace a furnace is reasonable, and a good company will not object.
When a furnace is worth replacing
All Island Comfort says replacement is usually worth considering when a furnace is over 15 years old, the repairs keep coming, the heat exchanger is cracked, or it is rated below 80% AFUE. The efficiency bands it uses match the Department of Energy’s.
| AFUE rating | What it means | Source |
|---|---|---|
| 56% to 70% | Older, low-efficiency system | Department of Energy |
| 80% to 83% | Mid-efficiency | Department of Energy, All Island Comfort |
| 90% to 98.5% | High-efficiency, condensing | Department of Energy |
If you replace, a ducted heat pump can use the same duct system. See heat pumps for what PSEG Long Island requires before it pays a rebate.
What to get in writing before the repair
- The diagnosis in plain words, and the part being replaced.
- The price before work starts. All Island Comfort gives upfront pricing before any repair.
- Whether the part is still under the manufacturer’s warranty, and whether the labor is covered.
- For a replacement, a written contract. New York’s Attorney General says home improvement contracts over $500 must be in writing, and you can cancel until midnight of the third business day after signing.