Furnace Troubleshooting: Common Issues and Their Solutions

Last updated on November 14, 2023

Troubleshoot your furnace with this guide to get your solutions to the most common issues. Read on!

The weather’s getting colder. Around the world, this winter has been the chilliest in generations. Add to the cold weather the ongoing cost of living crisis and you have a recipe for disaster.

Many Americans are unable to heat their homes due to rising energy costs. Because of this many people’s furnaces are breaking down. The less you use your furnace in winter the more likely it will be to freeze over.

Take the time to learn about common furnace issues and keep yours on as much as you can to prevent yours from breaking down; furnace breakdowns in the winter can be devastating.

Here’s everything you need to know.

Flame Sensor

furnace display

One of your furnace’s most important components is the flame sensor, a device that detects the presence of a flame. Unless this device is working, massive amounts of gas could be dumped into your home, creating a fire and explosion hazard.

It is essential that you learn to spot the signs of a broken one so immediate action can be taken in replacing a bad flame sensor and you can prevent gas from leaking out of your boiler, into your house.

Replacing a flame sensor is highly complex and should be left to the professionals.  

Low Pressure

furnace repair

A very common problem that can be resolved at home is low boiler pressure, caused usually by taps being left on overnight or faulty radiators. If you find your furnace has stopped working and shows an error code relative to low pressure, underneath your furnace turn the pressure valve.

This is usually a red valve located immediately below the furnace’s main body. Turn the pressure valve for just a few seconds to repressurize your furnace. Only turn the valve for a few seconds, as adding too much pressure can be bad for your boiler.


fixing gas furnace

High pressure is just as much of a problem as low pressure. In fact, it is arguably more of a problem as too much pressure can cause explosions.

Usually, your furnace will make a whirring noise if there’s too much pressure, or radiators will make a hissing sound every time they are turned on.

High pressure can be released by taking a radiator key and opening the pressure valve of the radiator nearest to your furnace. After a few seconds, water will begin spitting out and the radiator will stop hissing. If you release too much pressure, follow the tip given above and add more.

Frozen Pipes


In the winter, pipes freeze. If your boiler is not turned on and this happens it could leave you unable to heat your home until your pipes have thawed.

However, it doesn’t have to be this way; there is an easy fix you can use. Take your furnace’s waste pipe out of the wall and leave it sitting inside a bucket — water should begin coming out of it once it has defrosted. Then, your boiler will kick in and start working.

Only after the main pipes outside have thawed can you put the waste pipe back into the wall. If you do it before then, the water will back up again.

Pilot Light

If your furnace pilot light goes out, it will probably stop providing heat to your house. While extinguished pilot lights are usually easy to fix, you should hire a professional to make repairs for you.

The repairs mentioned so far can be conducted independently, save for the first. Making repairs to your boiler’s pilot light could invalidate your warranty, meaning if you are unable to fix that you won’t receive a new furnace.

Repairs should only ever be made by a trained contractor.

Furnace Leaking

If you notice that your furnace is leaking water then immediate action should be taken. As most people’s furnaces are powered by electricity, water freely flowing could cause serious damage.

If water gets into the wires powering your furnace then it could break. There are many different reasons why your furnace could be leaking water.

As referenced above, it’s wise to let a professional inspect and then fix this issue. Attempting to fix it yourself could invalidate your furnace’s warranty.

Cold Radiators

home radiator

Cold radiators in your house mean that your furnace isn’t working, especially if the heating is turned on. Cold radiators are just an indication that your furnace is not working, it is not a sign of any one particular problem.

Low pressure, a faulty pilot light, or frozen pipes can all cause cold radiators. On your furnace, an error code will display when it’s not working properly. Take this error code and refer to your furnace’s instruction manual.

Within this manual, you should find detailed instructions explaining what your furnace’s shown error code means and how to repair the issue.

Smelling Gas

If you smell gas, get out of your house immediately. A gas leak could lead to an explosion or fire. Once you have got out of your house, call the emergency services immediately, so they can dispatch a team and resolve the issue for you.

Most likely, your entire neighborhood will have to vacate their homes while the issue is fixed. Gas explosions can be devastating.

If you do not report a leak and an explosion occurs, you could be held accountable, if you are fortunate enough to escape unscathed, that is.

Other Fixes

As mentioned previously, if your furnace stops working then you will see an error code appear on its center console. Whenever you encounter problems with your furnace go and see if an error code is being shown.

If it is, then you can either refer to your furnace’s user manual and figure out what is wrong or you can turn to the internet. A lot of people find that turning to the internet when their furnace is not working is the most effective way of resolving their issues without having to pay an expensive plumber or repairman.

Only ever read guides written by those in the know, on specialist blogs. Research an author’s credentials before following their advice.

Learning to repair your furnace yourself will save you money. You will inevitably encounter problems with your furnace at various different points in your life, so learning to resolve these will prevent you from having to call out a repairman or activate your furnace’s warranty.

Only ever let qualified and experienced contractors near your furnace, as bad repair can invalidate its warranty.


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