Thermostat Says Heat On but Furnace Not Running? Check these Before Calling a Pro.

If your thermostat says “heat on” but the furnace isn’t running, the issue may be a tripped breaker, dirty filter, weak thermostat batteries, or an internal ignition failure. Start with safe homeowner checks like confirming thermostat settings and inspecting your air filter. If the furnace still won’t start, contact a licensed HVAC professional to diagnose and repair the problem.

If your thermostat says “heat on” but your furnace isn’t running, it’s frustrating — especially on a chilly night in Aurora or nearby areas like Richmond Hill, Newmarket, or King City.

Before calling for furnace repair, there are a few safe steps you can take to troubleshoot the issue. Here’s what you should check — and when it’s time to call a professional.

1. Check if the Thermostat Is Communicating with the Furnace

Just because your thermostat displays “heat on” doesn’t always mean it’s actually sending the signal.

✅ What you can safely do:

• Make sure it’s set to “Heat” mode, not “Auto” or “Cool.”

• Set the temperature higher than the current room temp.

• Replace the batteries if it’s battery-powered.

• For smart thermostats, check for Wi-Fi or power connection issues.

If none of this helps, the problem could be with the control board or thermostat wiring — that’s something only a qualified HVAC technician should handle.

2. Verify Power to the Furnace

If your furnace isn’t getting power, it can’t start — no matter what your thermostat says.

✅ Check your electrical panel:
Look for a tripped breaker labeled “Furnace” or “HVAC.” Reset it once if needed.
⚠️ If it trips again immediately, stop there — this could indicate a serious electrical issue that needs professional repair.

3. Make Sure the Furnace Switch and Door Are Secure

Many homeowners don’t realize furnaces have a power switch nearby (it looks like a light switch). Make sure it’s turned on.
Also, double-check that the front panel door is closed tightly. Most furnaces have a safety switch that won’t allow operation if the panel isn’t fully latched.

4. Check the Air Filter

A clogged air filter can cause your system to overheat or shut down.

✅ How to check:
Turn off the furnace, remove the filter, and inspect it. If it looks dark or dusty, replace it with a clean one of the same size.

Keeping your filters clean helps your furnace run more efficiently and prevents unnecessary wear.

5. Inspect the Pilot Light or Ignition System

If you have an older furnace, check whether the pilot light is on.
If it’s out — don’t try to relight it yourself unless you’re absolutely sure it’s safe and know your system’s process.

Newer furnaces use electronic ignition systems, which can fail due to sensor or wiring issues. These should only be repaired by licensed HVAC professionals.

⚠️ If you ever smell gas, turn off the furnace immediately and contact a professional.

6. When to Call a Professional

If your furnace still won’t start after these checks, it’s time to bring in the pros.
A qualified technician can diagnose issues with the control board, blower motor, ignition system, or safety sensors — safely and efficiently.

For reliable service in Aurora and nearby communities like Richmond Hill, Newmarket, King City, Whitchurch-Stouffville, Markham, and Vaughan, schedule an appointment for furnace repair or, if needed, furnace replacement.

Prevent Furnace Issues Before They Start

Routine maintenance can help prevent your furnace from leaving you in the cold. An annual inspection by a licensed technician ensures your system runs safely, efficiently, and reliably through the winter.

Need Help Getting Your Heat Back On?

If your thermostat says “heat on” but your furnace won’t start, don’t wait until your home gets uncomfortably cold.
Book a professional furnace repair in Aurora today to restore your heat quickly and safely.