Furnace Not Working? Check These 8 Things First

A furnace that suddenly stops is often something simple: a thermostat setting, a tripped breaker, a clogged filter, an empty fuel tank, or snow blocking the outside vent pipes. Work through the 8 checks below in order — they take about 10 minutes and solve a large share of no-heat calls. If you hit a stop warning, skip the rest and get help.

1. Thermostat

Set it to HEAT, a few degrees above the current room temperature, with the fan on AUTO (not ON). Blank or dim screen? Replace the batteries. Also check that a programmed schedule isn't overriding you.

2. Power

Find the furnace switch (it looks like a light switch, on or near the unit, and gets flipped by accident) and make sure it is ON. Then check your breaker panel and reset a tripped breaker once. If it trips again, stop — that's a pro call.

3. Filter

Slide it out and hold it to the light. If it is grey and packed, replace it. A clogged filter is the number one cause of furnaces overheating, shutting off, and short cycling.

4. Front panel

Make sure the furnace door is fully seated and latched. A safety switch keeps the unit off if it isn't — a common issue right after a filter change.

5. Fuel

Gas furnace: are your other gas appliances working? If not, it's the supply, not the furnace. Oil or propane (common outside Plattsburgh city): check the tank gauge before anything else — running dry during a cold snap is more common than people expect.

6. The snow check

High-efficiency furnaces breathe through two white PVC pipes on an outside wall. Drifting snow, frost, or an ice cap can block them, and the furnace shuts itself down for safety. Gently clear snow and ice from around the openings — never push anything into the pipes. During a heavy storm, re-check every few hours.

7. Vents

Open supply and return vents and keep them clear of furniture, rugs, and curtains.

8. Read the code, then reset once

Peek at the control-board window: a blinking light pattern is an error code, and the legend is printed inside the door panel. Write down the pattern BEFORE resetting — it saves the technician real diagnostic time. One power reset is fine. Repeated resets that keep failing mean stop and call.

Still no heat? Protect the house while you wait

• Open cabinet doors under sinks on exterior walls so room air reaches the pipes.
• Let faucets on exterior walls drip slightly if pipes are at risk of freezing.
• Space heaters: plug directly into the wall (no extension cords), keep clear space around them, and never leave them running unattended.