DIY troubleshooting 6 common gas furnace problems

As winter tightens its grip, having a cozy home warmed by your gas furnace is essential. But what if it doesn’t fire up like it should or starts making odd noises? Before you call in a technician, there are plenty of troubleshooting steps you can tackle yourself to sort out common furnace issues.

The advice in this article might not fit your exact appliance model. We aim to provide helpful tips for all kinds of DIY repairs, but variations in models can mean different troubleshooting steps, error codes, or parts needed. For the most accurate info, it’s best to check your manufacturer’s documentation or reach out to us with any questions.

1. Troubleshoot the thermostat

Double-checking your thermostat settings

Let’s start with the basics: double-check your thermostat settings. Is it set to “heat” mode, and is the temperature higher than the current room temperature? If your thermostat runs on batteries, they might be dead—replacing them could solve the issue. Also, give it a gentle cleaning to remove any dust or debris that could be affecting its performance.

Considering where your thermostat is located

Where your thermostat is placed can impact its accuracy. If it’s too close to heat sources like an oven or in direct sunlight, it might think your home is warmer than it actually is. On the other hand, drafts from windows or doors can make it read cooler. Moving the thermostat to a better location can help your furnace respond when it’s supposed to.

Testing the furnace fan

Set your thermostat to activate the furnace fan. If nothing happens, there might be a problem with how the thermostat connects to the furnace or an issue with the fan motor itself. Check the wiring for any obvious signs of damage or loose connections, it could be an easy fix.

2. Inspect air filters and vents

Checking and replacing air filters

A clogged air filter can block airflow, making your furnace work harder or shut down altogether. Find your furnace’s air filter, usually where the return duct meets the furnace, and take it out. If it’s dirty or covered in dust, it’s time for a new one. Replacing your air filter every month or so keeps things running smoothly.

Making sure vents and registers are open

Check that all the air vents and registers are open and not blocked. Sometimes furniture, rugs, or curtains can cover them up, affecting airflow and heating. Clearing the way helps warm air circulate throughout your home.

3. Check power and electrical connections

Looking at circuit breakers and fuses

Your furnace might be down simply because it’s not getting power. Check your home’s electrical panel to see if the furnace’s circuit breaker has tripped. If it has, reset it by flipping it off and back on. In older homes with fuses, check for any blown fuses and replace them if needed. If breakers keep tripping or fuses blow again, there might be a bigger electrical issue that needs attention.

Inspecting electrical connections

After confirming the furnace has power, check the unit at the electrical connections. Look for loose wires or connections that might need tightening. Pay attention to the control board, if you see any burn marks or scorching, the board might be faulty and need replacing. If you’re comfortable using a multimeter, you can test wires and switches for continuity to see if they’re working right. For parts like motor windings or heating elements, check their resistance values.

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4. Address gas supply issues

Making sure the gas valve is open

Your furnace needs a steady gas supply to run. Find the gas safety shut-off valve near your furnace and ensure it’s set to “on”, the handle should line up with the gas pipe. If there’s still no gas flow, check the main gas meter’s shut-off valve to confirm it’s open as well.

Looking at the pilot light

If your furnace has a pilot light, check if it’s lit. Your owner’s manual will have steps on how to safely relight it if needed. The flame should be a steady blue; a flickering or yellowish flame could mean issues like dirty burners or not enough oxygen.

5. Deal with noisy operations and unusual odors

Investigating strange sounds

Weird noises like banging, squealing, or rattling from your furnace aren’t normal and could point to mechanical problems. These might come from loose parts, a worn-out belt, or issues with the blower motor.  

Identifying odd smells

It’s pretty normal to smell something when you first turn on the furnace for the season, that’s usually just dust burning off. But if you notice strong or persistent odors like burning plastic or gas, that’s a red flag. Turn off your furnace and look into it. If it’s a gas smell, shut off the gas supply and call a professional right away.

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6. Solve short cycling and inconsistent heating

Troubleshooting short cycling

Short cycling happens when your furnace turns on and off frequently without heating your home properly. This could be due to a faulty thermostat, blocked airflow, or the furnace overheating. Start by checking where your thermostat is placed. Make sure air filters are clean and vents are open to keep air moving smoothly.

Fixing uneven heating

If some rooms are hot while others are cold, your furnace might not be spreading the heat evenly. Check that all ducts and vents are connected and free from blockages. Make sure the gas valve is working right and that gas lines aren’t clogged. Sometimes, you might need to adjust dampers in the ductwork to direct airflow where it’s needed.

Read more: 12 simple space heater safety tips for this winter

Additional help

If you need more help or replacement parts, swing by AppliancePartsPros.com. We’ve got a bunch of repair guides and quality parts to get your furnace humming again.

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