Furnace Won’t Start? 7 Things to Check Before You Call
When the temperature drops below freezing in Washington, D.C. or Maryland and your furnace won’t fire up, it’s easy to panic. Before you call for service, a few quick checks solve a surprising number of no-heat calls — and the rest tell us exactly what’s wrong.
Work through these in order. They’re safe for any homeowner, and they often get the heat back on in minutes.
1. Check the thermostat
Make sure it’s set to Heat and the target temperature is a few degrees above the current room reading. If it’s a smart or battery thermostat, a dead battery will leave the screen blank — swap the batteries and try again.
2. Confirm the furnace has power
Furnaces have their own switch that looks like a light switch, usually on or near the unit. It’s easy to flip off by accident while carrying laundry past it. While you’re there, check the breaker panel for a tripped breaker.
3. Look at the air filter
A clogged filter chokes airflow and can trip the furnace’s safety limit, shutting it down to prevent overheating. If your filter is gray and packed with dust, replace it. In our area, filters often need changing every 1–3 months during heating season.
4. Make sure the gas is on
If you have a gas furnace, confirm the gas valve is open and other gas appliances (like your stove) are working. If you smell gas at any point, leave the house and call your gas utility — don’t troubleshoot further.
5. Check the condensate drain
High-efficiency furnaces produce water that drains away as they run. If that drain or its float switch clogs, the furnace shuts off as a safety measure. A full drain pan is a clue.
6. Reset the furnace
Turn the furnace switch off, wait 30 seconds, and turn it back on. A single reset can clear a temporary fault. If it locks out again right away, stop — repeated resets on a unit that keeps failing can do more harm than good.
7. Inspect the vents and registers
Closed or blocked supply and return vents restrict airflow and can cause the same overheating shutdowns a dirty filter does. Make sure furniture and rugs aren’t covering them.
If you’ve worked through all seven and you still have no heat — or the furnace short-cycles, smells odd, or shows a blinking error code — it’s time for a professional. Our NATE-certified technicians diagnose and repair gas, electric, and oil furnaces fast. Request heating service.
All-Pro Services has kept homes warm across Washington, D.C. and Maryland for more than 40 years. Learn more about our heating repair and installation, or see the areas we serve.
Furnace Troubleshooting FAQs
Why does my furnace turn on and then shut off quickly?
That’s called short-cycling. The most common causes are a dirty air filter, a blocked vent, or an overheating safety limit. Replace the filter first; if it continues, have it inspected.
Is it safe to keep resetting my furnace?
One reset is fine. But if the furnace locks out repeatedly, a safety system is doing its job — keep resetting and you risk a bigger failure. Call for service instead.
How often should I change my furnace filter in winter?
Every 1–3 months for most homes during heating season, more often with pets or allergies. A clean filter is the single easiest way to prevent no-heat shutdowns.
What should I do if I smell gas?
Leave the house immediately, don’t touch switches, and call your gas utility from outside. Only return once it’s been declared safe. Then we can repair the furnace.