We’re so used to being comfortable at home that the HVAC is usually never thought about until there’s a problem. Our HVAC not working properly happened this winter, and here’s what we did to fix it.
Top-Lines
- 99% of HVAC not working is NOT DIY
- 1% of HVAC not working is DIY-able
- I know enough about HVAC to know when to call a pro
The HVAC Isn’t Really Working
Theresa: “Hey, Mark the thermostat is set to 69 degrees, but it’s 66 degrees. There’s no heat. It works sometimes, but it’s still cold in here. How about you use your home inspector training on this?”
Mark: “Ok, I’ll look at the unit. I’m not really sure what I’m looking for, but I’ll look.”
I took the panels off. Pulling the bottom panel on our unit releases a physical switch that signals the furnace to go through its start sequence. Like clockwork, the inducer fan kicked on, so that means it is getting a signal from the thermostat.
The heat element/glow plug–which can get dirty over time, but I had maintenance within the last year–glowed red. The gas valve opened and the gas ignited. It had a perfect blue flame (orange tips are bad).
Bingo. Maybe it was some weird glitch.
Three Weeks Later
T: “Hey Mark, the thermostat is set to 69 degrees, but it’s 64 degrees. It’s not running and it’s still cold in here.”
M: “Uh…”
T: “Wait. Some thermostats need batteries. Ours does. I changed them a few years ago, maybe that’s it.” “
It was.
Hint: It also wasn’t.
Two Weeks Later
T: “Hey Mark, the thermostat is set to 69 degrees, but it’s 64 degrees. It’s not running and it’s still cold in here. The batteries didn’t fix it.”
M: “Maybe it’s a problem at the furnace (Hint: It is). I’ll take a look, again.”
I pulled the panel covers and it fired right up. I closed the panel cover then went upstairs to watch football then stood next to a vent.
Bubkus. Some air came out but very little. What witchcraft is this?
Call the HVAC Pro
So the plumber I work with on various remodeling projects is also an HVAC specialist. And we’re buddies. We talk. Since the HVAC not working is a theme that I hadn’t solved….
I started writing all this “inducer” and “sequence” and “glow plug” in an email to him. And before I pressed “Send,” I heard him in my head say: Did you check the filter?
Damn you!
I hadn’t checked the filter. I meant to but I hadn’t.
Fearing total embarrassment, I removed and replaced the filter.
Guess what? We’re back in the game.

