Furnace Not Working? 11 Things to Check Before You Call for Furnace Repair in Sherwood Park
The first real cold snap in Sherwood Park is when most furnaces show their problems. You turn up the thermostat and get nothing, or cold air, or a furnace that starts and stops every few minutes.
The good news is that a lot of “broken” furnaces aren’t broken at all. A tripped switch, a clogged filter, or a vent blocked by frost can stop a perfectly healthy furnace. This guide walks you through the safe checks you can do yourself, explains what each symptom usually means, and tells you exactly when it’s time to call a professional.
Quick answer: why is my furnace not working?
The most common reasons a furnace stops working are:
- a thermostat setting or dead batteries,
- a tripped breaker or furnace power switch,
- a clogged air filter,
- a loose furnace door panel,
- a closed gas valve,
- or a blocked exhaust or intake vent.
Check these first. If the furnace still won’t heat, or shows a flashing error light, a failed part like the flame sensor, igniter, or control board is likely, and a licensed technician should diagnose it.
Safety first: stop and call right away if…
- You smell gas (rotten eggs). Don’t touch light switches or the thermostat. Leave the house, then call ATCO Gas’s 24-hour emergency line at 1-800-511-3447 or 911 from outside.
- Your carbon monoxide alarm goes off. Get everyone outside and call 911. Never ignore a CO alarm, even if nobody feels sick.
- You hear a loud bang or boom when the furnace starts. This can mean delayed ignition. Shut the furnace off and call a technician.
- You smell burning plastic or electrical odours, or see scorch marks. Turn the furnace off at the switch.
If none of these apply, you can safely work through the checklist below.
Furnace troubleshooting chart
| Symptom | Most likely cause | Try this first | Call a pro if… |
|---|---|---|---|
| Won’t turn on at all | Thermostat, power, door switch | Check settings, batteries, breaker, panel | Still dead after checks |
| Blowing cold air | Fan set to “ON”, dirty filter, ignition or flame sensor issue | Set fan to “AUTO”, change filter | Cold air continues |
| Turns on, then shuts off | Dirty filter, flame sensor, blocked vents | Change filter, clear vents | Keeps short-cycling |
| Flashing light on furnace | Error code | Count the flashes, check the chart on the door | Code points to a part failure |
| Burning dust smell | First start of the season | Let it run for an hour | Smell stays or smells electrical |
| Some rooms cold | Closed vents, blocked returns, dirty filter | Open vents, clear furniture | Rooms stay cold |
| Loud banging or squealing | Ignition or blower problem | Turn it off | Right away |
11 things to check when your furnace isn't working
1. Check the thermostat settings
Make sure the thermostat is set to HEAT, not COOL or OFF, and set at least 2–3 degrees above the current room temperature. On a programmable or smart thermostat, check that a schedule or “away” mode isn’t holding the temperature down.
2. Replace the thermostat batteries
A blank or dim screen often means dead batteries. Many thermostats won’t send a heat call on low batteries, even if the screen still shows something.
3. Check the breaker and furnace power switch
Your furnace has a switch that looks like a regular light switch, usually on or near the furnace. It gets flipped off by accident more often than you’d think. Also check your electrical panel for a tripped furnace breaker. If the breaker trips again right after you reset it, stop and call a technician.
4. Make sure the furnace door is closed tightly
Furnaces have a safety switch behind the front panel. If the panel isn’t fully seated after a filter change, the furnace won’t run. Push it firmly into place.
5. Change the air filter
A clogged filter is one of the top reasons furnaces overheat, shut off early, or blow weak air. As a general guide:
- Standard 1-inch filters: check monthly and replace every 1–3 months.
- Thicker 4–5 inch media filters: replace every 6–12 months.
- Homes with pets, renovations, or a lot of dust need more frequent changes.
6. Confirm the gas valve is open
Find the gas line going into the furnace. The handle on the shut-off valve should line up with the pipe (open), not sit across it (closed). If other gas appliances like your stove or water heater aren’t working either, contact your gas provider.
7. Read the blinking status light
Most modern furnaces have a small window with an LED light. The number and pattern of flashes is an error code. Count them, then match the code to the chart on the inside of the furnace door. Write the code down, because it helps a technician arrive with the right part.
8. Clear snow and frost from the exterior vents (a big one in Alberta)
High-efficiency furnaces vent through two white PVC pipes on the outside wall. After a heavy snowfall, drifting snow, or a deep freeze, these pipes can get blocked with snow or frost. The furnace then shuts itself off for safety.
Gently clear snow and ice from around both pipes, keep about a foot of clear space around them, and never cover them. If they ice up every winter, the venting may need to be corrected by a professional.
9. Check for a frozen or clogged condensate line
High-efficiency furnaces produce water that drains through a small plastic tube or pump. If the line is clogged, or freezes where it runs through a cold space, a safety switch can shut the furnace down. Look for water around the furnace, or a condensate pump that’s full or not running.
10. Listen for the ignition sequence
When the furnace starts, you should normally hear the inducer fan, then see the igniter glow or click, and then see the burners light.
- If it tries to light and stops after a few seconds, a dirty or failing flame sensor is a very common cause.
- If there’s no glow or click at all, the igniter may have failed.
- Both are routine repairs, but they involve the gas and ignition system. If you aren’t completely comfortable, let a licensed technician handle them.
11. Check vents, registers and cold air returns
Walk through your home and make sure supply vents are open and cold air returns aren’t blocked by furniture, rugs, or storage. Blocked airflow causes cold rooms, overheating, and short cycling.
What common furnace symptoms mean
Why is my furnace blowing cold air?
First check that the thermostat fan is set to AUTO, not ON. When it’s set to ON, the blower runs even when the furnace isn’t heating. If the fan is on AUTO and the air is still cold, the likely causes are a dirty filter causing the furnace to overheat and shut the burners off, a flame sensor problem, blocked vents, or an ignition failure.
Why does my furnace keep turning on and off?
Frequent on-and-off cycling (short cycling) is usually caused by a clogged filter, a dirty flame sensor, blocked PVC vents, a thermostat in a bad spot (near a heat source or draft), or a furnace that’s too big for the home. Short cycling wears out parts quickly and should be looked at if a filter change doesn’t fix it.
Is a burning smell normal when I first turn on the furnace?
Yes, within limits. A dusty burning smell on the first start of the season is normal and usually clears within an hour. If it doesn’t fade, or it smells like burning plastic, rubber, or wiring, turn the furnace off and call a technician.
Why is my furnace making loud noises?
Small clicks and a gentle whoosh are normal. Banging on startup, screeching, grinding, or rattling are not. They can point to delayed ignition, a failing blower motor or bearing, or a loose part. Shut the furnace off and book a repair to avoid a bigger breakdown.
Repair or replace? A simple way to decide
Most gas furnaces last about 15–20 years. As a rough rule of thumb, multiply your furnace’s age by the repair quote. If the result is over $5,000, replacement is often the better value. For example, a 16-year-old furnace with a $400 repair gives 6,400, which points to replacement.
Other signs it may be time to replace:
- repairs are becoming frequent,
- heating bills are rising,
- rooms heat unevenly,
- or the furnace is more than 15 years old.
Our guide on how long a furnace lasts in Sherwood Park goes deeper. If replacement makes sense, see our furnace replacement service and financing options.
What to tell your technician (so they fix it faster)
Before you call, note:
- the furnace brand and approximate age (on the label inside the door),
- any flashing light code,
- what the furnace does and when it started,
- any smells or sounds,
- when the filter was last changed.
This helps the technician come prepared and often means a faster, cheaper repair.
How to prevent your next furnace breakdown
Most mid-winter breakdowns start as small problems that a tune-up would have caught: a dirty flame sensor, a weak igniter, a clogged drain, or a worn blower. An annual furnace tune-up in Sherwood Park before the cold arrives is the easiest way to avoid a no-heat call at -30°C.
Between visits:
- change your filter on schedule,
- keep the exterior vents clear,
- keep the area around the furnace free of storage.
For a full seasonal checklist, see our winter furnace maintenance guide. If your furnace humidifier isn’t keeping up either, we also offer humidifier installation.
Frequently asked questions
Can I reset my furnace myself?
Yes. Turn off the furnace power switch, wait about 30 seconds, and turn it back on. This clears some lockouts. If the furnace locks out again, there’s an underlying problem that a reset won’t fix, so call a technician.
How long can I go without heat in winter?
Not long in Alberta. In extreme cold, a home can lose heat quickly and pipes can freeze in hours. If your furnace stops during a cold snap, call for emergency service. Our emergency HVAC repair guide explains what to do while you wait.
Is it safe to use space heaters while I wait for repair?
Use only certified electric space heaters, keep them at least 3 feet from anything flammable, plug them directly into the wall, and never leave them running unattended or overnight. Never use a gas stove, oven, or barbecue to heat your home.
How often should a furnace be serviced?
Once a year, ideally in early fall before the heating season begins.
What’s the most common furnace repair?
Dirty or failed flame sensors, igniters, clogged filters, and condensate drain problems are among the most common causes of no-heat calls.
Do you offer furnace repair outside Sherwood Park?
Yes. We serve Sherwood Park, Fort Saskatchewan, Ardrossan, and across Strathcona County.
Still no heat? We can help
If you’ve worked through these checks and your furnace still isn’t working, Sherwood Mechanical’s technicians can diagnose the problem and get your heat back on. Book furnace repair in Sherwood Park or contact us today, before the next cold snap.