Furnace Not Working? Answers from Lambton HVAC Experts

When your furnace stops working in the middle of an Ontario winter, it’s more than an inconvenience — it’s a comfort and safety issue. At Lambton Heating & Cooling, we understand how stressful that can be. That’s why we’ve answered the most commonly searched furnace-related questions homeowners ask when the heat goes out.

Whether it’s a minor fix or something more serious, this guide can help you troubleshoot — and know when to call the pros.

Why isn’t my furnace turning on?

If your furnace won’t start, here are some of the most common causes:

Thermostat is off or set incorrectly
Dead thermostat batteries
Tripped breaker or blown fuse
Dirty air filter restricting airflow
Pilot light or ignition system failure

What to try first:
Make sure the thermostat is set to “Heat” and the temperature is a few degrees higher than the current room temperature. Then check the breaker panel and your air filter.

If it still won’t turn on, contact Lambton Heating & Cooling — we’ll get your system running again quickly.

Why is my furnace blowing cold air?

If warm air isn’t coming from your vents, the issue could be:

The pilot light is out (for gas furnaces)
The air filter is clogged
The flame sensor is dirty
The fan is set to “ON” instead of “AUTO” on your thermostat

Quick tip:
Check your thermostat fan setting. If it’s set to “ON,” the furnace fan will blow continuously — even when the furnace isn’t heating — which can feel like cold air. Set it to “AUTO” to fix this.

If the issue persists, our technicians at Lambton Heating & Cooling can diagnose it quickly and recommend a solution.

Why does my furnace keep turning off and on?

This issue is called short cycling, and it can be caused by:

A dirty filter
An overheating furnace
A thermostat in the wrong location
A furnace that’s too large for your home

Short cycling wastes energy and puts extra stress on your system. Replacing your filter is a good first step. If that doesn’t solve it, book a service visit with Lambton Heating & Cooling so we can address the root of the issue.

How often should I replace my furnace filter?

This is one of the easiest ways to prevent furnace problems. A dirty air filter can:

Cause overheating
Reduce airflow
Lead to higher energy bills
Shorten your furnace’s lifespan

Filter replacement schedule:
Check your filter monthly and replace it every 1 to 3 months, depending on your home environment, pets, or allergies.

Need help selecting the right filter? Just ask our team — we’re happy to help.

Should I reset my furnace?

Yes — many furnaces have a reset button, usually located near the motor housing.

How to safely reset:

Turn off the furnace via the thermostat
Find the reset button (usually red)
Press and hold for about 10 seconds
Wait a few minutes and turn the system back on

Important:
If you’ve pressed the reset more than once with no result, stop. This may indicate a deeper issue that needs professional attention.

When should I call a professional?

You should call Lambton Heating & Cooling when:

Your furnace won’t start or keeps shutting off
It’s blowing cold air nonstop
You hear strange noises (banging, grinding, etc.)
You smell burning or gas
Your troubleshooting attempts haven’t worked

We offer fast, affordable, and reliable furnace repair and furnace installation services across Lambton County and surrounding areas — including emergency calls during harsh winter months. If your system is more than 10 years old and needed frequent repairs, it may be time to consider a furnace replacement.