Safety first — before any troubleshooting
Smell gas? Stop reading. Leave the building, leave the door open behind you, and call your gas utility's emergency line or 911 from outside — before you call us or anyone else.
Carbon monoxide alarm sounding? Get everyone out and call 911. Don't reset the alarm and don't go back in to investigate.
Everything below assumes neither of those is happening.
Now the part nobody tells you when you're standing in a cold house: a big share of no-heat and no-AC calls end with a switch, a breaker, or a filter — not a broken machine. Run the five-minute checks below before you book anyone. If they don't bring the system back, you've ruled out the simple stuff, and you can tell whoever you call exactly what you found. That makes the visit faster and the diagnosis cheaper.
No heat: the five-minute checks
- Thermostat is set to Heat and the set point is above room temperature — then try fresh batteries, because a dying thermostat fails quietly
- Furnace breaker is on at the electrical panel — if it tripped, reset it once and watch what happens
- Furnace power switch is on — it looks like an ordinary light switch, usually on or beside the unit, and it gets bumped more often than you'd think
- Filter isn't clogged — a packed filter overheats the furnace and trips its safety shutoff
- Pilot or ignition status, checked through the sight glass only — many furnaces blink an error code you can write down for the technician
If the burners light and then quit, or nothing happens at all, stop there. Modern furnaces lock themselves out after repeated failed ignitions for a reason — the fault is inside the cabinet, and that's furnace repair territory, not screwdriver territory. Call us at (555) 555-0123 and mention what the status light was doing; it usually narrows the problem down before we even arrive. One more thing worth knowing: if this is the second or third no-heat call this season, the pattern itself is a diagnosis — here's how to think about it if your furnace keeps failing.
No AC: the five-minute checks
- Thermostat is set to Cool with the set point a few degrees below room temperature
- AC breaker is on at the electrical panel — there are often two, one for the indoor unit and one for the outdoor
- Outdoor disconnect is on — the small box on the wall near the outdoor unit; a pulled disconnect after yard work is a classic
- No ice on the refrigerant lines or indoor coil — if you see frost, switch cooling off and let it thaw before anything else
- Filter isn't clogged — weak airflow is the most common reason a coil freezes in the first place
If the outdoor fan spins but the house never cools, or the breaker trips again the moment the compressor kicks in, leave the system off. Running it in that state can finish off a failing compressor — the single most expensive part in the machine. That's an AC repair visit, and it starts faster when you can tell us which of these checks failed. We answer at (555) 555-0123.
What not to do
Don't open sealed panels. Anything behind screws — the combustion chamber, the blower compartment, the control board — is sealed for a reason. There's live voltage, moving parts, and on gas equipment, flame. Opening it voids nothing if you just look, but the moment you start pulling connectors, you're creating the second fault.
Don't bypass safety switches. Taping down a door switch or jumping a limit switch turns a controlled shutdown into a hazard. The furnace didn't shut itself off to annoy you — a sensor saw something it didn't like.
Don't run an iced AC. Ice on the lines means the system is hurting itself with every minute of runtime. Off, thaw, then diagnose. And don't chip the ice off — fins and coils bend easily and they don't bend back.
Don't keep relighting a pilot that won't stay lit. It's going out for a cause, usually a failing thermocouple or a draft problem, and repeated attempts just fill the burner area with gas.
Be careful with space heaters. Plug them straight into the wall — never a power strip or extension cord — keep a meter of clearance from anything that burns, and turn them off when you sleep. Never heat the house with the oven, and never run anything fuel-burning (patio heater, camp stove, generator) indoors. That's how carbon monoxide gets people.
Protect your home while you wait
In winter, think pipes first. Water lines in exterior walls and cold basements can freeze and split long before the house itself feels dangerously cold. Open the cabinet doors under sinks on outside walls, let the faucet farthest from the water meter run at a pencil-lead trickle, and keep interior doors open so the remaining warmth circulates. If the house will sit empty and cold for more than a day, shut off the main water valve and open the lowest tap to drain the lines — a burst pipe costs far more than the heating repair.
In summer heat, people come before comfort. Close blinds on the sun side, move everyone to the coolest room in the house, run fans across damp skin (a fan plus a spray bottle is a genuinely effective cooling system), and keep water going. Babies, seniors, anyone on certain medications, and pets all overheat faster than healthy adults — check on them, and never leave anyone in a parked car while you sort the AC out.
Call right now if any of these are true
No heat in freezing weather
Pipe-burst risk and indoor temperature both get worse by the hour. This is a call-now job, day or night.
The breaker trips again right after a reset
That's an electrical fault, not bad luck. Leave it off and stop resetting.
Burning or electrical smells from the unit or vents
Shut the system down at the breaker first, then call.
Water around the furnace or indoor unit
Shut it down. Water plus live electronics escalates quickly.
Infants, seniors, or medical conditions in the home
Extreme indoor temperatures turn dangerous fast for vulnerable people. Don't wait it out.
The same failure keeps coming back
Repeated lockouts or short cycling after the basic checks means a real fault is being masked, not fixed.
When it's a call-now emergency
If the five-minute checks didn't bring it back, the fault is inside the equipment — and the fastest way out is a phone call, not more troubleshooting. The next step is to call 24/7 emergency service: dial (555) 555-0123 any hour, tell us what you checked and what the system did, and we'll take it from there.
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Common questions
This guide is general information about industry standards and typical practice — not site-specific professional advice. Requirements vary by jurisdiction; confirm what applies to your property with your local authority having jurisdiction (AHJ) or with our team. See our Terms of Service for details.