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How to Troubleshoot Common Furnace Issues

Written on: December 1, 2025

Johnny Prescott Helps You Stay Warm All Winter

furnace Contoocook, NHA cold snap in New Hampshire is no time to discover your furnace isn’t working. Before you find yourself shivering and searching for emergency repair services, it’s helpful to know that many common furnace issues can be resolved with simple troubleshooting.

As the go-to experts for furnace maintenance and repair in Contoocook, NH, and the Greater Concord area, the team at Johnny Prescott Oil & Propane knows a thing or two about keeping homes warm and comfortable.

A malfunctioning furnace doesn’t always mean a costly repair is on the horizon. Often, the problem is something you can identify and fix yourself in just a few minutes. Understanding these basic checks can save you time, prevent a service call, and give you peace of mind. This guide will walk you through the most common furnace problems and how to troubleshoot them safely.

Fixing 5 Furnace Problems

When your heat goes out, a bit of panic can set in. But before you pick up the phone, run through this quick checklist. These simple steps can often get your system back up and running without needing a professional.

1. Check Your Thermostat

It might sound obvious, but the thermostat is the command center for your heating system, and it’s a frequent source of issues.

  • Is it set to “Heat”? Make sure the thermostat is switched to the heating mode. It’s easy to forget it’s still on “Cool” or “Off” from a warmer day.
  • Check the temperature setting. Is the set temperature higher than the current room temperature? Your furnace won’t turn on if the room is already warmer than the thermostat’s setting.
  • Look at the batteries. Many modern digital thermostats are battery-powered. If the screen is blank or showing a low battery indicator, replacing the batteries might be all you need to do.

2. Inspect the Furnace Power Switch

Your furnace has its own power switch, which looks like a standard light switch. It’s usually located on or near the furnace unit itself. This switch can sometimes be turned off by mistake, especially if it’s in a high-traffic area like a basement. Ensure the switch is in the “On” position.

3. Examine Your Circuit Breaker

If the power switch is on but the furnace still isn’t running, the next stop is your home’s main electrical panel. A power surge could have tripped the circuit breaker connected to your HVAC system.

  • Locate the breaker labeled “Furnace,” “Heater,” or “HVAC.”
  • Check its position. If the breaker is in the “Off” position or stuck in the middle, flip it completely off and then back on to reset it. If it trips again immediately, this signals a more serious electrical problem that requires a professional technician.

4. Ensure Your Fuel Supply is Adequate

Your furnace can’t produce heat without fuel.

  • For oil furnaces: Check the gauge on your oil tank. If it’s empty or very low, you’ll need to schedule a fuel delivery.
  • For propane furnaces: Check the gauge on your propane tank. If it reads low, it’s time for a refill.

Running out of fuel is a common reason for a furnace to stop working, so always keep an eye on your levels, especially during the colder months.

5. Check for Clogged Filters

A dirty or clogged air filter is one of the most frequent causes of furnace malfunctions. A blocked filter restricts airflow, which can cause your furnace to overheat and shut down as a safety precaution.

  • Locate and inspect your filter. They are typically located inside the furnace or in the return air duct.
  • Replace if necessary. Disposable filters should be changed every 1-3 months. If your filter is visibly dirty, replacing it could solve your problem and will improve your system’s efficiency and your home’s air quality.

The Best Fix is Prevention

While troubleshooting can resolve minor issues, the most reliable way to avoid furnace breakdowns is through regular, professional maintenance. An annual furnace tune-up from a qualified technician does more than just prevent unexpected failures. It ensures your system runs at peak efficiency, which can save you money on energy bills and extend the lifespan of your equipment.

During a tune-up, our technicians at Johnny Prescott inspect and clean all the critical components of your furnace, identify potential problems before they escalate, and make sure your system is operating safely. It’s a small investment that delivers significant returns in reliability and peace of mind.

If you’ve worked through these troubleshooting steps and your furnace is still on the fritz, don’t hesitate to reach out. Our team is ready to provide the expert furnace repair services you need to restore warmth and comfort to your home.