What Should You Do First When the Heat Goes Out?
Before you pick up the phone, spend ten minutes on a short checklist: thermostat batteries and settings, the furnace breaker, the gas shutoff valve, the air filter, and, for boilers, the water level. Roughly a third of no-heat calls we run in Greater Boston trace back to something a homeowner can safely check themselves.
When a January nor’easter drops temperatures into the single digits, a dead heating system feels like an emergency, and sometimes it is. But West Roxbury, Roslindale, and Dedham homeowners call us every winter for problems that turn out to be a tripped breaker or a thermostat with dead batteries. The checklist below walks through what to check, in what order, and, just as important, exactly when to stop and call a professional instead.
Is It the Thermostat, Not the Furnace?
Start at the wall, not in the basement. Confirm the thermostat is set to Heat, not Cool or Off, and that the setpoint is at least 3-5 degrees above the current room temperature. If the display is blank or dim, replace the batteries, most digital thermostats run on two AA or AAA cells and die without warning, often overnight when the house is coldest. If you have a smart thermostat, check that it hasn’t lost its Wi-Fi schedule or slipped into an “away” mode. After any change, wait five full minutes: many thermostats have a built-in compressor and short-cycle delay before they call for heat.
Did a Breaker Trip or a Switch Get Bumped?
Every furnace and boiler has a service switch that looks exactly like a light switch, usually mounted on or near the unit or at the top of the basement stairs. Kids, movers, and holiday-decoration boxes flip these all the time. Check it, then check the electrical panel for a tripped breaker, it will sit between On and Off. Reset it once, firmly to Off and then On. If it trips again, stop. A breaker that trips repeatedly is protecting you from a real electrical fault, and resetting it over and over risks damage or fire. That’s a call to a technician, not a DIY project.
Is Gas Actually Reaching the Unit, and Is It Safe to Check?
Look for the gas shutoff valve on the pipe feeding the furnace or boiler. The handle should be parallel to the pipe (open), not perpendicular (closed). Quickly confirm another gas appliance, the stove, for instance, lights normally, which tells you gas service to the house is on.
Safety first, always: if you smell gas, that rotten-egg odor, do not check anything else. Do not flip any switches on or off, do not use your phone inside, and do not try to find the leak. Leave the building immediately, and from outside call your gas utility (National Grid or Eversource, depending on your neighborhood) and 911. Gas leaks come before every other step on this list, and they are never a DIY item.
What Can You Learn by Watching the Ignition Sequence?
With the thermostat calling for heat, stand near the furnace and watch through the sight glass or louvers. On a modern furnace you should hear the inducer fan spin up, see the hot surface igniter glow orange, then see burners light with a steady blue flame. If the igniter glows but no flame appears, or the burners light and cut out within seconds, you likely have an igniter, flame sensor, or gas valve issue, useful detail to give whoever answers the phone at furnace repair. On older equipment with a standing pilot, check whether the pilot is lit; relight it only if you’re comfortable and the manufacturer’s instructions are printed on the unit.
Could a Clogged Filter or an Empty Oil Tank Be the Culprit?
A filter packed with dust can overheat a furnace until its high-limit switch shuts the burners down, the blower may run, but the air comes out cool. Pull the filter and hold it up to a light; if you can’t see light through it, replace it. Filters cost $10-$30 and should be changed every 1-3 months in heating season.
Oil heat? Check the tank gauge. Gauges stick, so if it reads low or you’re unsure, rap the tank gently and listen for the hollow sound of an empty tank. Running an oil tank dry usually means the burner needs priming after the delivery, mention it when you call.
What About Steam Boilers, the Classic Boston Problem?
Boston’s triple-deckers and pre-war homes run on steam more than almost any American city, and steam boilers have one check all their own: the water level. Find the sight glass on the side of the boiler, the water should sit roughly halfway up. If it’s empty, the low-water cutoff has done its job and shut the burner down to prevent a dry-fire, which can crack a cast-iron section. Add water slowly via the fill valve only if the boiler is cool; adding cold water to a hot, empty boiler can crack it. If the boiler needs water every few days, you have a leak or a failing auto-feeder, and it’s time for boiler repair before something expensive lets go.
Which Symptoms Are Safe to Troubleshoot Yourself?
| Symptom | Likely Cause | DIY-Safe? |
|---|---|---|
| Blank thermostat display | Dead batteries or tripped breaker | Yes, replace batteries, reset breaker once |
| Blower runs, air is cold | Clogged filter, failed igniter, limit lockout | Partly, change the filter, then call |
| Boiler sight glass empty | Low-water cutoff tripped, possible leak | Cautiously, add water only when cool |
| Breaker trips repeatedly | Electrical fault in motor or wiring | No, stop resetting and call |
| Rotten-egg gas smell | Gas leak | No, leave, call the utility and 911 from outside |
When Should You Stop and Call a Professional?
Here’s the honest line between homeowner territory and technician territory:
- Gas smell: leave the building first, utility and 911 before anyone else, including us.
- Repeated breaker trips or burning smells: electrical faults get worse, not better.
- Boiler that dry-fired or needs constant water: hidden leaks damage the boiler and the house.
- Short-cycling burners or a screeching blower: running it “until it dies” often triples the repair bill.
- Anything involving opening the burner compartment beyond observation, combustion adjustments require instruments, not intuition.
If your ten minutes are up and the house is still cold, Boston Comfort Systems dispatches same-day when the schedule allows, and our $99 diagnostic fee is waived when you approve the repair. Estimates on replacement equipment are always free, call us before you spend a night under every blanket in the house.