Why Is My Furnace Not Keeping Up With The Thermostat?

Ossiana Tepfenhart
by Ossiana Tepfenhart

If you are like most people, you occasionally will want to turn your thermostat up or down a notch. When you do, you probably are going to expect your furnace to react to the switch fairly quickly. Sometimes, though, you might notice that your furnace isn’t as quick to react as it once was. Did you ever wonder what’s going on with that issue?

The most likely reason why your furnace is not keeping up with the thermostat is a dirty filter. Begin by cleaning or replacing your furnace’s filter. If the problem persists, it may be due to a faulty thermostat, an overheating furnace, or a bad sensor. Check the issue immediately to avoid any potential fire hazard.

Having a laggy furnace or a nonresponsive furnace is a pain, but it’s something you have to deal with as soon as possible since it can be a fire hazard. This guide will help you understand what you should expect when you’re tackling this issue, as well as a little more about each possible cause.

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Why Won’t My Furnace React To Thermostat Changes?

There are a number of reasons that this can happen, each of which requires its own fix. To make things easier for you, we’re going to help arrange them based on the way you should troubleshoot your furnace.

A Bad Thermostat

The first thing you should do is check your thermostat. Is it receiving electricity? Is it properly wired? Old or nonresponsive thermostats are the most common cause of a nonresponsive furnace. Thankfully, this is a relatively easy fix. All you need to do is buy a new thermostat to replace the defective one.

An Overheating Furnace

This is the next issue that you should check, and it’s a doozy. If your furnace shuts off before your rooms reach their desired temperature, this is an indicator that your furnace’s safety system is kicking in as a result of overheating. An overheating furnace is a serious fire hazard and has to be addressed immediately.

There are several reasons why a furnace could overheat, including bad sensors, filthy filters, or a dysfunctional motor. The best way to handle this is to turn your furnace off and talk to a repairman immediately. You should never use a furnace that is in danger of overheating, since it could mean an explosive ending to your home.

A Bad Sensor

Every furnace operates through the use of a furnace sensor that tells the HVAC system what’s going on with the heat. Your furnace sensor looks like a little white rod with a metal tip at the end, and it’s usually placed through the furnace box. Take a look at the sensor. If it’s cracked, tarnished, or corroded, you need a new sensor. If it’s just dirty, clean it off and see what happens.

The good news here is that a bad sensor is an easy DIY fix and also happens to be a cheap part to replace. A typical furnace sensor only costs $5 to $50 to replace on your own, with high-end, brand-specific sensors being the most expensive option.

A Dirty Filter

With any furnace, the air that gets circulated in your home will have to be pushed through a filter. This ensures that your home is filled with clean air and also helps keep the furnace safe from the elements. Unfortunately, filters get dirty over time. The dirtier your filter is, the more effort it will take to push air through the filter.

The extra trapped air can cause your furnace to overheat as well as experience slowdowns from all the trapped dirt and dust. So, if you need help with your furnace, it’s a good idea to change your filter. In many cases, this quick fix is more than enough to make your furnace catch up to your thermostat alone.

How Often Should I Replace A Furnace Filter?

Experts agree that the vast majority of homeowners don’t replace their furnace filters frequently enough. To make sure that your furnace keeps working, it’s best to replace the filter at least once a month. If you live in a high-pollen or high-pollution area, you should replace it even more frequently.

What Else Could Cause My Furnace To Be Unresponsive To A Thermostat?

Though the four main reasons are the most common explanations for a laggy furnace, there are other reasons why you might have this occur. Some of the less common reasons include:

  • You might have the wrong furnace size. If your furnace is too small for your home, then it will take a while for the air to travel to every room. Sometimes, you might even have a room that never gets heat. After all, a small furnace could never be able to heat Buckingham Palace.
  • Your exterior vent might be blocked. During the winter, a lot of animals might try to find refuge from the cold near the exterior vent. Make sure that it’s not covered with leaves or a nest, since your furnace needs ventilation to work properly. If the furnace detects a blockage in the vent, safety measures might kick in and stop its functions.
  • If you have an energy-efficient furnace, clean out your drain lines. A cloggy or grimy drain line can make it difficult for a furnace to generate enough heat for your home.
  • Your furnace might’ve blown a fuse. This is another common reason why. Just replace the fuse.
  • There is also a chance that your furnace blower motor has gone bad. Though this doesn’t necessarily mean you have an unresponsive furnace, it can make it hard to get the warm air generated by the furnace to travel to the rooms at a decent speed.
  • Lastly, make sure you actually turned the furnace on. Though rare, I’ve heard of people who forgot to turn their furnace on after a quick repair. Check to make sure it’s actually on first.

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Related Questions

Why is my furnace fan blowing out cold air?

If you notice that your furnace fan is blowing out cold air, this is a problem that’s typically caused by a dirty filter. The filter is too dirty to let hot air pass through, which traps it in the HVAC system. This leads to an overheating furnace, which triggers safety measures that shut the system down.

How can I tell if my furnace is broken?

If you notice odd smells, hear strange noises coming from the furnace, or can’t seem to keep the furnace on, call your HVAC specialist. These all suggest that something is wrong with your furnace.

Can a furnace explode?

Though exploding furnaces were fairly common back in the earlier part of the last century, improvements in HVAC tech made sure risks are minimal. While they still can explode, there are now dozens of safety shutoff switches that help prevent an explosion or a fire from occurring. Statistically, furnaces are a lot safer than space heaters.

When should I replace a furnace?

The general rule of thumb is that a furnace should be replaced when it’s 15 years of age or older. Additionally, if your furnace has a repair that’s greater than a third of its cost, it may make more financial sense to replace it. This is especially true when you take into account the energy savings that a new furnace can bring.

Ossiana Tepfenhart
Ossiana Tepfenhart

Ossiana Tepfenhart is an expert writer, focusing on interior design and general home tips. Writing is her life, and it's what she does best. Her interests include art and real estate investments.

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