Furnace Won’t Turn On? 6 Checks for Downriver Michigan

Short answer: If your furnace won’t turn on, check six things in order: thermostat settings, power (breaker and furnace switch), air filter, condensate drain line, ignition system, and fuel supply. Work through them in order — they cover the most common reasons a furnace won’t start. If you’ve checked all six and it’s still dead — or you see water, smell gas, or it keeps tripping — stop and call a pro.

First cold snap of the season in Downriver — Saturday night drops into the upper 40s, and furnaces across Trenton, Wyandotte, Woodhaven, and Riverview are firing up for the first time since spring. Run through these six checks before you call anyone — you might fix it yourself in five minutes.

1. Check the Thermostat

Start here — it’s the simplest fix and resolves a surprising number of “furnace won’t turn on” calls.

• Set to HEAT, not COOL or OFF
• Fan set to AUTO, not ON (ON runs the blower constantly, including blowing cool air between heating cycles)
• Temperature set 3–5 degrees above the current room temp
• Replace the batteries if the display is dim or blank

2. Check the Power

Furnaces have more than one power source, and any of them can be the culprit:

• Breaker box — look for a tripped breaker labeled furnace/HVAC. Flip it fully off, then back on.
• Furnace power switch — there’s usually a regular light-switch-style toggle on or near the furnace. It gets bumped off more often than anyone admits, especially in basements used for storage.
• Blower door panel — if the front panel isn’t seated correctly, a safety switch cuts power. Make sure it’s latched.

If the breaker trips again immediately after you reset it, stop — that’s an electrical problem, not a furnace problem. Call someone.

3. Check the Air Filter

A clogged filter chokes airflow. Restricted airflow overheats the heat exchanger, a high-limit safety switch trips, and the furnace shuts down to protect itself.

Pull the filter out and hold it up to a light. If you can’t see light through it, that’s your problem — or at least part of it. Swap in a new one (note the size printed on the frame and the airflow arrow direction).

If the filter’s been in there since spring, this is a likely culprit on the first cold night of the season.

4. Check the Condensate Drain Line

This one only applies if you have a high-efficiency furnace (90% AFUE or higher — white PVC vent pipes instead of a metal chimney). These units produce gallons of water a day when running, and it all drains through a small condensate line.

Two failure modes:

• Clogged line or full drain pan — algae and sludge build up over summer. Many units have a float switch in the drain pan or pump that kills the furnace when water backs up. Clear the line, empty the pan, and it may fire right back up.
• Frozen line — a Michigan deep-winter problem. If any section of that drain line runs through an unconditioned space — attic, crawlspace, along an exterior wall — it can freeze solid when overnight lows drop into the 20s. Water backs up, the pressure switch can’t close, and the furnace shuts down without ever firing. You’ll usually see an error code or a blinking light on the control board.

A frozen or backed-up drain is a service call: thaw the line, clear the trap, and reroute or protect the exposed section so it doesn’t happen on the next freeze.

5. Check the Ignition

If the furnace has power, the thermostat’s calling for heat, the filter’s clean, and the drain is clear — but you hear it try to start and fail — you’re looking at an ignition problem.

• Older furnaces with a pilot light: is the pilot lit? If it’s out, follow the relighting instructions printed on the furnace door panel. If it won’t stay lit, the thermocouple is the usual suspect.
• Newer furnaces with electronic ignition: listen for the click of the ignitor. No click, or a click with no flame, points to a failed ignitor or flame sensor — both common culprits and quick for a tech to replace.

Ignition components are not DIY territory beyond the pilot light. Gas, electricity, and combustion in one box — let a tech handle it.

A dirty flame sensor is exactly what took us out on a no-heat call in Flat Rock — cleaned it, tested the furnace, and had the customer’s heat back on in no time. It’s a small part that causes a big problem.

6. Confirm the Fuel Supply

Last check, and it matters more than people think: is the gas valve to the furnace open? (Handle parallel to the pipe = open.) If you had work done over the summer, someone may have shut it off and forgotten.

If you smell gas at any point — rotten egg smell — don’t touch anything electrical, don’t light anything, leave the house and call the gas company first.

When to Stop Troubleshooting and Call a Professional

You’ve hit the limit when:

• The furnace still won’t run after all six checks
• The breaker trips again after resetting
• There’s water pooling where it shouldn’t be
• You smell gas (leave the house, call the gas company)
• The same shutdown keeps happening on cold nights
• Anything involving the gas valve, control board, or heat exchanger

A cracked heat exchanger is the serious one — it can leak carbon monoxide. If your CO detector goes off, get out and call 911, then call us.

In Trenton, Wyandotte, Woodhaven, Riverview, or anywhere Downriver — we’re 24/7 for no-heat calls. Emergency furnace repair here.

Gibraltar homeowners — here’s what furnace repair looks like in Gibraltar.

Frequently Asked Questions

My furnace runs but blows cold air — is that the same problem?

Related but different. Cold air usually means the burner isn’t firing while the blower runs — check the thermostat fan setting (AUTO not ON) first, then the ignition items in check #5. If the burners fire and the air is still cold, you may have a ductwork or airflow issue.

How much does a furnace repair cost?

Here’s what we typically charge in the Downriver area — parts and labor included:

• Service call / diagnostic: $99 ($159 after hours)
• Ignitor replacement: $200–$300 (depending on model)
• Thermostat replacement: $200–$600 (depending on the thermostat)
• Blower motor replacement: $600–$1,200 (depending on motor)
• Inducer motor replacement: $650–$1,500 (depending on motor)
• Control board replacement: $300–$1,000 (depending on model)
• Gas valve replacement: $250–$600 (depending on valve and gas pipe work)

As a rough rule of thumb, if a repair quote approaches half the cost of a new furnace — especially on a unit over 15 years old — it’s worth talking replacement instead.

Should I keep resetting my furnace when it shuts off?

No. A lockout is a message, not a malfunction — repeatedly clearing it erases the fault history a technician would use to find the real problem, and can turn a minor fix into a major one. One reset to check, then diagnose or call.

Why does my furnace always break on the coldest night?

Because that’s when every marginal component gets stressed at once — and problems that developed over summer (clogged filter, sludged drain line, weak ignitor) only show up under full load. A fall tune-up catches most of this before the deep freeze.

Is it normal for a high-efficiency furnace to make water?

Yes — completely normal. Condensing furnaces pull so much heat from exhaust gases that water vapor condenses out. Several gallons a day in cold weather. That water has to drain somewhere, which is exactly why the condensate line matters.

Bottom Line

Six checks: thermostat, power, filter, condensate line, ignition, fuel. Run them in order before you call anyone. If the filter’s been in since spring, start there — it’s the classic first-cold-night culprit.

— Justin Alexandrou, Owner, Downriver Climate Control