Furnace Won’t Run on Generator? 3 Common Causes + Fixes


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When the power goes out, the last thing you want is to struggle with cold air entering your home. This is why many people hook a furnace up to a portable generator, allowing them to continue enjoying heat throughout their home even when there is no power. However, when a furnace doesn’t run on a generator, you find yourself in a difficult situation. 

When the furnace doesn’t run on a generator, take a look at the system’s wattage, make sure there is a bonding between the ground and neutral power lines, and see if the generator uses inverted power. 

This post helps you understand why a furnace will sometimes fail to run when plugged into a generator. We also give you the most effective solutions for each case. 

The Furnace Does Not Work With Inverted Power

Once you turn the furnace on, only to find that the generator is not supplying it with power, you may feel frustrated. It is important to start with the basic reasons why this may happen. Begin by comparing the furnace’s functions and power requirements to the features offered by the generator. 

You may find that there are certain functions that the furnace relies on or something it is not compatible with – which means the generator does not meet the needs of the HVAC system. 

Many generators use inverted power solutions to deliver efficient levels of electricity to your devices.

Unfortunately, this is also an area where you may face compatibility issues. The thing is, not all furnaces are compatible with inverted power. Some rely on standard power, and when the generator uses an inverter to convert power to AC, then the furnace may not power on when connected to the generator. 

How To Fix

The fix for this issue depends on the type of generator you have. Look at the model number and brand name. Now, see if you can find some information – such as a manual. You should have received a manual with the generator if you bought it new. 

The manual should give you details on whether or not an inverter is used in the generator. If you see that the generator uses inverted power, check to see if this is the problem – consider the power requirements of the furnace you use. 

Sometimes, it may be possible to switch the inverter on or off. If your generator allows for such a setting, try switching it off. Now, try to start the furnace again and see if that solves your issue. 

If the generator does not have an off switch for the inverter, you will probably need to get a different generator. 

It would be a good idea to see if you can find another generator just for testing purposes. Perhaps a friend owns a generator that does not use inverted power. Try this generator on the furnace and see if the problem is fixed. 

No Bonding Between Neutral and Ground

Another possible reason for a furnace not running on a generator may be related to the bonding between the neutral and ground lines. This issue is more common than you might think.

When you buy a new generator, particularly the more portable ones, you will often find that there is no connection between ground and neutral. This is a problem, as the furnace uses this bonded connection as a safety measure when it is turned on. 

In this particular situation, you may find that no power runs through the furnace at all. You may have other devices connected to the generator, and they all run effectively without any issues. 

How To Fix

While a common problem, the fix may not be as easy as you hope it would be. This is because the issue lies within the generator – particularly in the electrical wiring found inside the device. 

If you want to bond neutral and ground lines, it means you will have to open up the generator and work inside. If you have previous experience working with electrical systems and wiring, then you could attempt to do this yourself. 

You need to find both of these lines – neutral and ground. Then you need to find an appropriate method for bonding the two. When you attempt to do this, make sure you turn the generator completely off before opening it up or touching any of its wires. 

After bonding the lines for ground and neutral, put the cover of the generator back on. The next step is to connect the generator to the furnace again and then power it on. See if this process fixed the problem you ran into. If it does not provide you with a fix, then the reason the furnace won’t run on the generator lies with another area of the system. You will need to do more investigation to help you determine why this is happening. 

Incompatible Generator Wattage

Sometimes, the issue behind a furnace not running on a generator can be fixed. This allows you to continue using the same generator without a need for a replacement. However, there are scenarios where the generator does not work with the furnace. 

This is why you need to pay close attention to all factors related to the generator and your furnace when shopping. If you already have a generator but not a furnace yet, consider buying a furnace compatible with the generator. If you have a furnace but need to buy a generator, consider the generator’s functions and ensure it complies with the furnace’s requirements. 

How To Fix

In this particular scenario, you want to consider the wattage output of the generator. Then, you want to look at the furnace and its wattage requirements. Do the two figures match up? If not, then this might be where your problem lies. 

Take note that the generator can have a higher wattage rating than what is needed by the furnace. This will be the case in the majority of situations. There are, however, some portable generators that provide just enough power for basic devices. This generally also means the generator will have a low wattage rating. 

The fix here would not include making a change to the generator to allow more power to flow out to the furnace. Instead, you might have to consider a replacement for either the main furnace module or the generator. 

Before you do this, do take note of one thing – some generators come with adjustable power. This is often described as an “eco” mode. When the “eco” mode is turned on, a lower wattage is provided to connected devices, but it means the generator uses less fuel to generate power. 

If your generator has an eco mode, try turning it off – then see if it provides adequate power for the furnace to start. If the problem remains, then look at the best option for a replacement. If the generator is still new, you might be lucky enough to get it exchanged for a larger model, with the condition that you pay any additional fees. 

Summary

Generators are incredibly useful when the power is out, but they do have their limitations. While it may be tempting to hook the furnace up to the generator, you should ensure compatibility before investing. 

If you run into a problem where the furnace won’t run on a generator, then get a professional to inspect your setup. Sometimes, problems that you skip when investigating can be easily picked up by an HVAC expert. Fill the form below this article, and we’ll help you connect to a local professional.

Vincent Steele

Vincent is a freelance writer based in Santa Ana, California. When he isn't writing articles for Temperature Master, he can be found biking or hanging out with his cat, Shelly.

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