Did the heat stop work? Furnaces can stop running for all kinds of reasons. Sometimes, you might just have to tweak your thermostat or change your air filter. It’s not a big deal.

But other times, well. Let’s just say the problem could be a bit more complicated.

Oh, who are we kidding? It could be a lot more complicated.

When the problem is tricky to solve, there are a few common furnace parts that we’re quick to check. In our experience, they’re the ones that are most likely to go bad and prevent the furnace from heating. Let’s go over what they are.

But first! There are a few things you might want to check.

Before assuming your furnace suffers from one of the issues we’re about to cover, we recommend a little self-troubleshooting. Many furnace issues are simple to fix! They include:

  • Changing the temperature on your thermostat
  • Opening all your air registers (or unblocking them if they’ve been covered up)
  • Replacing a really dirty air filter
  • Resetting a tripped breaker
  • Resetting the power disconnect switch (if it got turned off)
  • Ensuring the gas control valve is open
  • Manually lighting your pilot light (older furnaces, primarily)

If you checked all of those things and your furnace still won’t heat, there’s a good chance one of the following problems is the culprit.

Your hot surface igniter went bad

Modern furnaces don’t have a pilot light. Instead, they have a device that starts the flame for heating. It’s called a hot surface ignitor, and it saves you from the hassle of manually lighting a pilot light.

But in many furnaces, it’s one of the first components to fail.

Whenever someone calls us to see why their furnace isn’t working, the hot surface ignitor is one of the first components we check during our troubleshooting process. If yours has gone bad, you’ll have to replace it.

Note that customers with HVAC service agreements can avoid this common problem. A technician will verify that your hot surface ignitor functions properly during your regular HVAC inspection.
Typically, your HVAC contractor will stock the hot surface ignitor your system needs. A technician can install it straight away, so you don’t have to keep living without heat.

There’s a clog in your fan motor pressure switch

In most furnaces, there’s a pressure switch that verifies that your vent pipe is free from blockages. If the vent pipe is clogged, this switch trips and prevents the fan motor from coming on.

In other words, it stops your furnace from running if the unit can’t vent properly. It’s a check on your health and safety as much as an operational performance feature.

That’s all fine and good, but the switch itself is also prone to get clogged. There’s a little hole in part of the switch assembly that can become clogged with debris and trips the switch. When this happens, the switch “tells” the furnace that the vent pipe is blocked. That’s not true, of course. The vent pipe is usually fine. Someone just needs to clean out the switch.

It’s kind of like when you burn the french fries a little bit and your smoke alarm goes off. There’s no fire, but you still have to deal with some loud beeping.

When you have this problem, we usually have to remove the inducer fan motor and clean it to remove any debris that might be blocking the hole. After that, you’re usually good to go.

Those are two of the most common furnace problems. But there’s a third.

And it’s one we mentioned earlier: a dirty air filter.

If your furnace is struggling to keep your house warm and you don’t remember the last time you replaced your air filter, that could be the problem. Dirty air filters won’t usually shut your furnace down completely — although they can cause a breakdown in extreme cases — but they will reduce airflow, overwork the system, and lead to costlier operation and performance deficiencies.

We see really dirty air filters all the time when servicing furnaces that aren’t keeping homeowners comfortable. And yes, in some cases, all it takes is a filter replacement to make the furnace heat the home properly again.

Got a problem with your furnace? We can help.

First, check all of the stuff we mentioned earlier, including your air filter!

If the furnace still won’t run (or won’t perform as well as it used to), that’s when you should get in touch with us. Whether you have a bad hot surface ignitor, a blockage in the pressure switch, or some other issue entirely, we can properly diagnose the issue and point you to the best solution.

company icon