3 Reasons Your Furnace Isn’t Getting as Warm as It Should – These Quick Fixes from HVAC Pros Will Save Your Winter Nights

There is nothing worse than switching on your heating on a freezing winter's day and realising that your furnace is not heating as it should. A struggling system can leave rooms chilly, energy bills high, and your patience wearing thin.

You don't have to call a pro right away, however. There are some small things you can check first to fix the problem yourself.

These are the most common reasons your furnace isn't heating correctly, and what you can do about it to make heating more efficient and restore your comfort.

3 Common Reasons Your Furnace Isn’t Heating

1. Blocked Filters

Eli Zimmer, CEO at Luxaire HVAC Services, begins, 'One thing I would definitely check is the filter – if it hasn’t been cleaned or replaced in a while, there could be significant buildup which could then be prohibiting the furnace from working at its normal capacity.'

This is the simplest furnace maintenance check you can do as a homeowner to avoid breakdowns. You can find furnace replacement filters on Amazon in several sizes to suit any furnace, with next-day delivery, so you do not have to struggle to heat a home if the power is out for too long.

'You could also check and clean vents around your home,' he adds, 'to see if those need to be cleaned too, so that air is flowing out easily.'

2. A Dead Thermostat

There are several common thermostat problems that could be the cause of a furnace not heating properly, especially if the filters are clean.

Dan Cronen, HVAC expert at SupplyHouse, asks, 'Does it need new batteries? It will tell you if it does. What has changed around it? The thermostat has a built-in thermometer, and when it “feels” colder than the temperature you’ve set it at, it switches the heat on.

'If it’s picking up heat from all the Thanksgiving cooking, it will think all is warm and well. If a space heater is plugged in right next to it, that will throw off its reading. Even TVs and electronics put out enough heat to throw off a temperature reading, so if the kids just plugged in that new TV and Xbox they got from Santa next to the thermostat, it could be messing with your thermostat.

'If you do find that something is throwing your thermostat reading, just turn the temperature setting up. People get unreasonably attached to their number on the thermostat, forgetting that the point is to keep them comfortable. If it’s cold where you are but not at the thermostat, turn it up!'

Knowing where to put a thermostat and relocating it (especially if it's close to a built-in vent or radiator) can also help long-term. It is a simple thermostat mistake to avoid for a warmer home.

If you have a smart thermostat, such as the Google Nest thermostat from Amazon or the Honeywell thermostat from Best Buy, check that it is connected to your boiler and sending the correct signals to turn on and off. The brand troubleshooting page should be able to help you with this, depending on which model you have.

3. The Sensor is Dirty

Matt Gorbacz, founder and indoor air quality specialist at Clean Air Technologies, explains, 'Another common issue is a dirty flame sensor or dirty burners. When they get covered in dust, the furnace keeps shutting off early, and the heat doesn’t stay on long enough to warm the house properly.'

This is the result of a safety mechanism designed to shut the furnace off and prevent a gas buildup when it cannot detect a lit flame.

'Now, you can try cleaning a flame sensor if you know where it is,' Dan says. You can do this by removing the sensor and cleaning it with steel wool or a scouring pad from Amazon. 'However, if the furnace keeps short-cycling even after cleaning, do call in a professional, as you don’t want to mess with gas parts.'

When to Call an Expert

Dan warns, 'Beyond this, you get into more technical waters. Maybe the furnace is having problems coming on or staying on. Older units may have a pilot light that needs to be relit, but they stopped making them decades ago at this point, so that’s less and less common.

'Modern units will likely have a control board that will actively give you an error code if you know where to look and how to decipher it.'

If the three basic checks haven't solved the issue, it is always safer to call a professional and have your HVAC system serviced. This keeps both you and your home safe from potentially catastrophic damage.

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If your furnace is working, but your home feels cool, check your insulation and draft proofing to make the heat go further. Beyond that, try the free trick to make radiators heat up faster and unblock vents to keep your home warm without turning up the heat.