HVAC Failure in Winter: What to Check Before You Call

If your heat quit during a cold snap, run five checks before you call anyone: the thermostat, the breaker, the filter, the condensate switch, and the outdoor unit. Our technicians find that a meaningful share of winter no-heat calls end at one of those five, and you can check all of them in about ten minutes. If the system is truly down, this guide also covers how to heat safely while you wait and what information gets a technician to you faster.

The ten-minute triage: step by step

1. Thermostat first. Replace the batteries if the screen is dim or blank. Confirm the mode is Heat, not Off or Cool, and set the target five degrees above the room temperature so the system has a clear reason to run. If the screen is completely dead with fresh batteries, the problem may be power to the system itself, which is the next step.
2. Breakers and switches. Check the furnace or air handler breaker at the panel, and reset it once if tripped. Then find the service switch near the furnace. It looks exactly like a light switch, and it gets flipped off by accident more often than anyone admits. Heat pumps also have an outdoor disconnect near the outdoor unit worth a glance.
3. The filter. Pull it out and hold it up to light. A clogged filter chokes airflow, overheats the furnace, and trips a safety limit that shuts everything down. If it is gray and packed, replace it, then give the system thirty minutes, because some limit switches need time to reset.
4. The condensate switch. High-efficiency furnaces produce water, and a float switch shuts the system down if the drain pan fills or the line clogs. Look for standing water in or around the drain pan near the furnace. If you find it, clear the drain line and empty the pan, and the switch resets itself.
5. The outdoor unit, if you have a heat pump. Light frost on the coil is normal in our damp winters. A unit encased in solid ice is not. Check that nothing is blocking airflow, like leaves or a slid tarp, and read the next section before you do anything about ice.
6. The gas supply, if you have a gas furnace. Are other gas appliances working? If the water heater and range are also dead, the problem is gas supply, not your furnace.

Heat pump iced over: what is normal and what is not

Heat pumps frost up by design in cold, damp weather, which describes most Puget Sound winter mornings. The system handles it with a defrost cycle: every so often it reverses briefly, warms the outdoor coil, and melts the frost. During defrost you may see steam rising off the unit and hear a whoosh as it switches. That steam is normal and is regularly mistaken for smoke. What is not normal is a coil buried in solid ice, ice sheets on top of the unit, or a unit that stays frozen all day. That points to a failed defrost cycle, low refrigerant, or a drainage problem. Do not chip at the ice, because the coil fins bend and puncture easily. Switch the thermostat to emergency heat if you have it, and make the call.

Safe temporary heat while you wait

Space heaters carry real fire risk when they are used casually, so use them deliberately. Keep three feet of clearance from anything that burns, including bedding, curtains, and furniture. Set the heater on a hard, level floor, never on carpet piles or a table. Plug it directly into a wall outlet, never into an extension cord or power strip, which overheat under that load. Turn it off when you leave the room and when you sleep. If you are buying one, pick a model with tip-over and overheat shutoff.

Two absolute rules. Never use a gas oven or range to heat the house, and never bring a grill, camp stove, or patio heater indoors. All of them produce carbon monoxide, and CO deaths spike in exactly this situation. Beyond the heater, shrink the problem: close off unused rooms, gather everyone into one warm room, layer up, and during a hard freeze open cabinet doors under sinks on exterior walls and let a faucet drip so a heating outage does not become a plumbing emergency too.

Who to call, and what speeds up dispatch

When you call, a few details get you scheduled faster and get the right parts on the truck. Know your system type: gas furnace, heat pump, ductless, or electric. Read the brand and model from the label on the cabinet. Describe the symptom precisely: no air at all, cold air blowing, short bursts that shut off, or unusual noise. Mention any error code, since many furnaces blink a light in a pattern visible through a small window on the cabinet, and heat pump thermostats often show a code. And say what you already checked, because ruling out the thermostat, breaker, filter, and condensate switch saves the technician the first fifteen minutes.

Our heating repair team handles furnaces, heat pumps, and ductless systems across the Puget Sound. If the failure hit outside normal hours, our after-hours repair page explains how we handle urgent calls, and our emergency diagnostics service covers how we pin down a failure fast. If your furnace runs but keeps shutting off after a few minutes, that pattern has its own set of causes, covered in our guide to why furnaces short cycle.

Common questions

My heat pump is blowing air that feels cool. Is it broken?

Maybe not. Heat pumps deliver supply air around 85 to 95 degrees, which warms the house steadily but feels cool against your skin, since skin temperature is about 90 degrees. If the house is holding its set temperature, the system is doing its job. If the temperature keeps falling, then something is wrong.

Is it safe to run a space heater overnight?

No. Turn it off when you sleep, even a newer model with safety shutoffs. Heat the bedroom before bed, then rely on blankets. A heater running unattended next to bedding for eight hours is the classic house fire scenario.

My furnace starts, runs a few minutes, then shuts off. What is that?

That pattern is called short cycling, and the usual suspects are a dirty flame sensor, a clogged filter, or a failing limit switch. It deserves a repair visit either way, because every failed cycle stresses the ignition components a little more.

When is no heat a true emergency?

When someone vulnerable is in the house, like an infant, an elderly person, or anyone medically fragile, or when indoor temperatures are heading low enough to freeze pipes. In those cases say so when you call, because it changes the dispatch priority. Otherwise a same-day or next-day repair with safe temporary heat is usually the right path.

What to do next

Run the five checks, and if the system is still down, get safe heat going in one room and make the call. Start at our emergency page if you are triaging more than one problem, or reach our heating team directly. Call (206) 970-1031, where real people answer early and late, every day, or book online. Have your brand, model, and symptoms ready and we will get warm air moving again.