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Why Your Furnace Won’t Turn On

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Gas furnaces are incredibly efficient, and highly reliable most of the time. However, just like any other mechanical system, they can have problems from time to time. Although a malfunctioning boiler may not be a serious problem in the warmer months, come winter it can be incredibly worrying. Especially if it’s your home’s main source of heat and hot water.

If you live in an area where temperatures drop below freezing at night, having a faulty boiler can be dangerous. Not only will your home have no heat and the internal temperature will drop, but your property’s pipes will be at risk of freezing. When pipes freeze, they are then at risk of bursting, causing internal property flooding. So, it’s important to work out what the problem is as soon as possible so that it can be dealt with and fixed. The last thing you want in the cold winter weather is to be left without heat.

To help you to do that, below are some potential reasons why your furnace won’t turn on. Along with tips for working out which of these is causing the problem. Of course, you could choose to call out an electrician. However, the things listed below are exactly how an electrician would go about checking for a problem. So, by going DIY, you can save yourself some money.

Circuit Breakers

Even furnaces that are run on gas or propane may rely on electricity for running certain components. Some furnaces have electronic ignitors, for instance, and some thermostats require power to run. Believe it or not, the newer your system is, the more prone to power-related problems it is. Smart thermostats, for instance, are especially prone to these problems.

To check the furnace’s electrical input, you will need to check the electronic components throughout the house. If these aren’t working, give your electric company a call, as this could be a sign of a more serious problem.

If the other components in your home are working, the chances are it’s an isolated problem. Check the circuit breaker for your furnace and ensure that they are switches to the ‘ON’ position. You can find these in your circuit breaker panel.

The next step is to check the circuit breaker on the furnace itself, or a switch beside your furnace. If any of these are in the wrong position, reset them. If the circuit trips again, this is a sign of a more serious issue, so it’s best to call an expert. Whatever you do, don’t tape the switches into the ‘ON’ position.


If the problem isn’t the circuit, the next area to focus on should be the thermostat itself. Sometimes, when a thermostat loses power, it will lose its programming and reset to its default settings. This means that your heating preferences will be erased.

If this appears to be the problem, check to make sure that the thermostat is back on and that it’s in ‘Heating’ mode. Reset up the thermostat by inputting your temperature settings – this should fix the issue. Once you’ve done this and your thermostat is back to normal; your furnace should start functioning again.

Check Drain Pan

If the problem isn’t the thermostat, the next step is to check the drain pan. Each furnace has a condensate pan – aka a drain pan, this collects any water that has been removed from the air by your furnace. Many people don’t realize it, but just like air conditioners, furnaces also produce condensation. So most furnaces have a float switch and a condensation pump. If these are working properly, any water should be drained out. However, if the pump isn’t working properly, it could lead to standing water.

The first thing that you need to do is check that the drain is clear. There are special tablets that you can use to help keep your furnace’s drain clear, preventing problems. If the drain isn’t clear, clean it, to make it usable again.

If your furnace is fitted with a pump, it will have a float switch. The float switch should be in the ‘down’ position, else your furnace won’t be able to run. So you will need to clean it and check how it runs, to see if the problem is fixable. If it’s not, you’ll need to replace it with a new pump. Until the float switch is in the right position, your furnace won’t run.

Check the Air Filter

If the problem isn’t the drain pan, the next step is to check the air filter. In order for your furnace to run properly, the air filter should be replaced on a regular basis. If this hasn’t been done, then a clogged air filter could automatically turn off your furnace for safety reasons.

Check your air filter and see how it looks. If it’s dirty, then this could be the cause of the problem. Replace the filter and see what happens. If your furnace begins working again, then this was the problem. If not, the issue is caused by something else, and you’ll need to move onto the next step.

Check the Blower Motor

The next part of your furnace to check for problems is the blower motor. This is quick and easy to do. All you need to do is go up to the little window on your furnace and see whether there is a green light in place. If you can see the light, this means that there isn’t a problem with the blower motor. However, if it’s not there or is doing odd things, it might be best to call in an expert.

Check the Pilot Light

If your furnace is ultra modern and doesn’t have a pilot light, you can skip this step. However, if your furnace does have a pilot light, this is an important step.

The pilot light on a furnace demonstrates that the gas or propane flow to it is working. If the light goes out, the flow of gas will stop, and so, the furnace will no longer work. To get the furnace working again, all you need to do is relight the pilot light – there should be a button for doing this on the exterior of the furnace. If you can’t find it, call in an electrician, and they should be able to fix the issue.

Check Gas/Propane Supply

If your furnace still isn’t working properly, the next step is to check the supply of gas or propane that your furnace is getting. The best method of doing this is checking another household appliance that uses gas, such as the cooker, for instance.

See whether your stove ignites, and you can tell whether it’s an isolated problem or something more serious. If your stove doesn’t light, call an expert immediately to come and look at your home’s gas supply and what’s going on.

If however, the gas in the rest of your home is working but not the supply to your furnace; this could be caused by something like a broken gas valve. Unless you know what you’re doing, it’s best to call in a professional to deal with this.

Check Ignitor Sensor

Last but not least, check your ignitor sensor. The ignitor sensor is the part of the furnace that tells your furnace whether there is a flame in there. It’s a safety feature that helps to ensure that your furnace only ignites when it’s safe to do so.

How it works is that the ignition sensor tells the furnace when it senses a flame – unless a furnace has a flame, it won’t turn on. While, for the most part, the ignition sensor works well, over time it can get dirty. When this happens, it will no longer function properly. This means that it may not sense the flame, and so, the furnace won’t turn on. If this happens, the ignition sensor needs to be cleaned. Then, the furnace should begin working properly again.

Although not helpful now, in the future aim to get your furnace checked once a year. By scheduling maintenance checks, you can not only ensure that your furnace is in good condition, but also that it’s safe to use. Having your furnace checked over can help to prevent further problems and keep it running for longer.

When your furnace won’t turn on, and you don’t know what the cause of the problem is it can be frustrating and stressful. Especially if the weather is cold and you’re worried about the impact a lack of heat will have on your family and your home. However, it’s important to be patient and take the time to work out the problem by process of elimination. Remember, there are only so many different things it can be – it’s just a case of working through them to determine what the problem is being caused by. Once you’ve determined what the issue is, you can then have it fixed. Then, hopefully, your furnace will begin to work properly again. Providing your home with an adequate source of heating for the colder winter months.

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