Furnace won't turn on in a Michigan cold snap: what to check first

Checks you can make safely

Start with the thermostat, and take a photo of its display and of any lights on the furnace before you touch anything; a picture is easier to describe over the phone than a memory. Confirm it is set to heat, that the set temperature is above the room temperature, and, if it runs on batteries, that the batteries are fresh. A blank screen is a clue worth passing on to whoever you call.

Next, power. A furnace has a service switch that looks like an ordinary light switch, usually on or near the unit, and it is easy to knock off. Check that it is on, and look at the breaker panel for a tripped breaker. Reset a tripped breaker once. If it trips again, leave it off and tell the technician, because a repeating trip means something is wrong that resetting will not fix.

Then the filter. ENERGY STAR advises changing or cleaning filters monthly, and a clogged one is a plain reason for poor heating. If you have not looked at yours in months, now is the time.

That is the whole list. We give no repair steps beyond it, and nothing about ignitors, sensors or burners, because we have no Michigan source on them and the work belongs to a professional.

Do these in order, and stop at the first one that changes something. If the furnace starts and then quits again within the hour, do not keep repeating the cycle. Note when it stopped and what you could hear, because a pattern of starting and quitting is what a technician asks about first.

A cold snap is when everyone’s furnace is working hardest, and it is also when companies are busiest. Running through the checks before you call costs a few minutes and sometimes saves a visit, but if the house is already cold and anyone in it is elderly, an infant or unwell, skip ahead to calling and do the checks while you wait.

Vents and flues

DTE’s safety checklist says to unblock furnace room air vents, because appliances need proper air flow to burn fuel completely, and to inspect the flues of appliances to make sure they are corrosion-free, securely attached and correctly vented. From inside the house you can do the first part: look at whether boxes, laundry or stored items sit against the furnace room vents.

If a flue has come loose or looks corroded, do not push it back yourself. Turn the furnace off at the switch and ask a professional to look, since a flue carries exhaust out of the house.

A pilot light that keeps going out

Older gas furnaces use a pilot flame, and many newer ones do not. If yours has a pilot and it has gone out, DTE’s gas safety page says: “Contact a licensed professional if the pilot flame of an appliance goes out. The professional should relight the appliance for your safety.” That is advice from one Michigan gas utility, and it is the only relight guidance we can source. We would not relight it from instructions found elsewhere, and the label on the furnace is written for that exact model.

If you smell gas or a CO alarm sounds

Stop troubleshooting. Leave the building and do not switch lights, use phones or flames inside to find the cause. DTE tells customers to call 911 from a safe place and then its Gas Leak Hotline at (800) 947-5000. Consumers Energy says the same order: 911 first, then 800-477-5050. Both say not to go back in until first responders or the utility say it is safe.

If a carbon monoxide alarm sounds, DTE says to leave the building and get into fresh air, then call 911. Consumers Energy says to leave right away and call 911. Our guide to carbon monoxide alarms and furnaces covers what the state advises about alarms.

Keep the house from freezing

A dead furnace in January turns into a plumbing problem fast. The State’s MiReady page says pipes in crawl spaces and attics are the most susceptible to freezing. If you are away, it advises setting the thermostat no lower than 55 degrees.

If a pipe does freeze, shut off the water at the main valve. Never use a torch or open flame on it. A hair dryer may thaw it, starting near the faucet, and if nothing comes out, call a plumber.

Do not heat the house with fuel-burning devices meant for outdoors. Consumers Energy says never to use a generator, grill, camp stove or other fuel-burning device inside your home, basement or garage, or near a window. CDC advice, as we read it, is to run generators outdoors more than 20 feet from windows, doors and vents. We read the CDC half through a summary, so treat it as a rule of thumb and follow the utility’s wording.

If the bill is part of the problem

A furnace that is working but unaffordable is a separate question from one that is dead, and Michigan has rules for winter shutoffs. Our guide to winter shutoff protections in Michigan explains what the state plan says and where to get help.

When to call, and what to have ready

Call when the checks above change nothing, when you smell gas, or when the house is losing heat faster than you can protect it. The emergency HVAC page explains how to ask for a match when the heat is out, and the furnace repair page covers the non-urgent case. We do not promise a response time, and no company’s availability is something we can vouch for.

Before you call, find the furnace’s model and serial number on the data plate, usually inside the cabinet door or on its side. Write down what you already tried, whether the blower runs, whether you hear clicking, and when the trouble began. A tech can use all of it, and none of it needs a tool.

When a company arrives, ask for its license number, then check it as described in how to find a licensed HVAC contractor in Michigan. Michigan’s home solicitation rule lets you cancel a door-to-door sale for three business days, with an exception for requests made without delay in an emergency.