What to Do If Your Furnace Stops Working During a Snowstorm

First: the situations that are not troubleshooting problems

Before anything else, rule these out. If any of the following applies, stop reading and act.

• You smell gas, or anything like rotten eggs or sulfur — leave the home immediately with everyone inside, avoid switches, appliances and phones while indoors, and call your gas utility or 911 from a safe distance.
• You see smoke or fire — get everyone out and call 911.
• Anyone has a headache, dizziness, nausea, confusion, unusual drowsiness or flu-like symptoms that improve outdoors, or a carbon monoxide alarm has sounded — get everyone and any pets outside into fresh air and call 911 from outside. Do not re-enter to investigate.

Carbon monoxide is colorless and odorless, which is why symptoms and alarms matter more than what you can sense. Our carbon monoxide safety guide explains detector placement and what to watch for.

Safe checks a homeowner can make

If there is no gas smell, no smoke and no sign of carbon monoxide, these checks are safe and resolve a meaningful share of no-heat calls. None of them requires opening anything energized or touching a gas component.

1. Confirm the thermostat is set to HEAT. Modes get bumped, especially on wall-mounted units near light switches, and AUTO or OFF will not call for heat.
2. Confirm the set temperature is above the current room temperature. If the display shows 68 and the room is 68, the furnace has no reason to run. Raise it a few degrees and listen.
3. Replace thermostat batteries if your model uses them. A low battery can leave a display lit while the thermostat no longer controls reliably.
4. Check the furnace service switch. It looks like an ordinary light switch on or near the furnace, and it gets flipped off by accident more often than you would expect — during storage, cleaning or a basement project.
5. Check the electrical breaker. Find the breaker labeled for the furnace or air handler. If it is tripped, switch it fully off and then back on once. If it trips again, stop and call — a repeating trip is an electrical fault, not a nuisance.
6. Inspect an accessible filter. If the filter slot is easy to reach and the filter is grey and matted, replace it. A heavily loaded filter can cause the furnace to overheat and shut down on its limit control.
7. Make sure supply registers and return grilles are open and clear. Furniture, rugs, boxes and holiday decorations block airflow, and blocked airflow can shut a furnace down.
8. Confirm the furnace access panel is fully closed. A door switch prevents operation when the panel is not seated, and a panel bumped loose will stop the furnace cold.
9. Look at outdoor vent terminations if you can do so safely. On high-efficiency furnaces, two plastic pipes exit through a sidewall, and drifting snow can block them. Clear snow only if you can reach the area safely from the ground without climbing, and never reach into the pipes.

That is the complete list. Our troubleshooting guide covers the same checks in more detail, and furnace won't turn on walks through a total no-response situation.

What not to attempt — ever

Some repairs are dangerous for anyone without training, tools and testing equipment. During a storm the temptation to try is higher, and the consequences are the same as any other day.

• Do not work on the gas valve or any gas piping
• Do not adjust burners or attempt to clean or align them
• Do not bypass or jumper a flame sensor, pressure switch, limit switch, rollout switch or door switch
• Do not perform live voltage testing inside the furnace
• Do not attempt any repair involving the heat exchanger
• Do not attempt to light burners manually on a furnace with electronic ignition

These controls exist to shut the furnace down before a dangerous condition develops. A furnace that keeps locking out is protecting you, and the answer is to find out why — not to defeat the control.

Keeping everyone warm safely while you wait

• Close off unused rooms and gather everyone into one or two smaller, interior spaces that are easier to keep warm
• Close blinds and curtains after dark to slow heat loss through windows, and open south-facing ones during daylight
• Layer clothing and use blankets and sleeping bags — trapped air next to the body is more effective than raising the thermostat on a furnace that is not running
• Check on older adults, infants, anyone with a medical condition and pets more frequently, since they lose heat and tolerate cold less well
• Keep exterior doors closed and use draft stoppers at the bottom of doors if you have them
• Eat and drink normally — warm drinks and food help the body maintain temperature

Safe portable heater considerations

Electric space heaters can bridge a gap, but they cause fires every winter when used carelessly. If you use one, use it carefully.

• Plug the heater directly into a wall outlet — never into an extension cord or power strip
• Keep at least three feet of clearance from bedding, curtains, furniture, clothing and paper
• Place it on a hard, level surface, never on carpet edges, rugs or furniture
• Turn it off whenever you leave the room or go to sleep
• Choose a unit with tip-over and overheat shutoff protection
• Do not run several heaters on the same circuit — overloaded circuits are a fire risk

Never use a gas oven or range to heat a home, and never bring a charcoal grill, camp stove, propane heater intended for outdoor use or a generator indoors or into an attached garage. Each of these produces carbon monoxide in an enclosed space, and this is one of the most common causes of serious poisoning during winter outages.

Protecting plumbing during a prolonged loss of heat

If heat is out for an extended period during freezing weather, pipes become a real concern — particularly those in exterior walls, unheated basements, crawl spaces and garages.

• Open cabinet doors under kitchen and bathroom sinks so warmer room air reaches the supply lines
• Let a small trickle of cold water run from the fixture farthest from where the water enters the house; moving water resists freezing
• Keep the garage door closed, especially if water lines run through that space
• Know where the main water shutoff is before you need it
• If a faucet stops producing water during a cold period, suspect a freeze and do not apply an open flame to thaw a pipe under any circumstances
• If a pipe bursts, shut off the main water supply immediately and then call a plumber

When professional emergency service makes sense

Call rather than wait when any of these describes your situation.

• You worked through the safe checks and the furnace still will not produce heat
• The furnace attempts to start repeatedly and locks out
• The breaker trips again after you reset it once
• The blower runs continuously with cool air only
• Indoor temperature is falling and outdoor conditions are severe
• Anyone in the home is medically vulnerable to cold
• You are seeing or hearing something that concerns you and you would rather have someone look at it

There is no prize for waiting out a storm without heat. A furnace that is locking out has identified a problem, and finding out what it is beats guessing while the house cools.

24/7 Emergency Furnace Service

Furnace Repair Fort Collins CO provides 24/7 emergency furnace service for homeowners in Fort Collins and nearby Northern Colorado communities.

Call 970-638-2717.

Call now for a FREE QUOTE and for service availability. Please have your 5-digit ZIP code ready.

Our emergency furnace repair page explains how urgent calls are handled and what to expect. If the furnace is producing no heat at all, furnace not heating covers the most common causes.

What to have ready when you call

Good information on the phone makes the visit more efficient and sometimes resolves the issue before anyone drives out.

• Your address and five-digit ZIP code
• What the furnace is doing — silent, running without heat, starting then stopping, or making an unusual noise
• How long it has been out and the current indoor temperature
• Whether you have already changed the filter, checked the breaker or reset anything
• Whether there is a carbon monoxide detector in the home and whether it has sounded
• The furnace brand and, if visible, the model number from the data plate

Before the next storm

1. Keep a spare filter of the correct size on hand.
2. Make sure carbon monoxide detectors are installed near sleeping areas and test them.
3. Know the location of the furnace service switch, the breaker panel and the main water shutoff.
4. Keep flashlights, batteries, blankets and a fully charged phone accessible.
5. Schedule furnace maintenance before the heating season rather than during it.
6. Save 970-638-2717 in your phone so you are not searching for it in the dark.