Furnace Clicks But Won't Ignite? What the Clicking Means
Click. Click. Click. Then nothing — or a fan that runs cold and shuts off. That sound is the furnace trying to light and giving up. It usually means the furnace is getting power and the thermostat is calling for heat; the problem is in the ignition sequence.
Safety first: if you smell gas, don't keep trying to start the furnace. Don't flip switches. Leave the house and call your gas company from outside.
What the clicks are
Most modern furnaces light in a sequence: the inducer fan starts, a pressure switch confirms it, the igniter glows or sparks, gas opens, flame proves, the main blower starts. The clicking you hear is a relay or spark igniter firing. If the furnace clicks and quits, one step in that chain didn't get its "OK."
You don't need to open anything to narrow it down.
1. Is the gas on?
Is anything else gas in the house working — stove, water heater, dryer? If nothing gas works, the problem is your supply, not the furnace. That's a call to the gas company.
Also check the furnace's own gas valve on the pipe leading into it: the handle should be in line with the pipe (parallel = open, crossways = closed). Only touch it if it's clearly a simple lever; if you're unsure, leave it.
2. The filter
A badly clogged filter can cause overheating on the previous cycle, tripping a safety that blocks the next ignition. Hold the filter to the light; if you can't see through it, replace it and wait 15 minutes.
3. The exhaust and intake outside
High-efficiency furnaces vent through white PVC pipes on the side of the house. If they're blocked — snow, ice, a bird nest, leaves — the pressure switch won't confirm and the furnace won't light. Clear them. Never seal or cap them.
4. Reset it once
Turn the furnace's power switch (the light-switch-looking one on or near the furnace) off, wait 30 seconds, turn it on. Many furnaces lock out after a few failed ignition tries and need a reset. Once. If it clicks and quits again, stop — repeated attempts can flood the burner area with gas.
When it's a pro
If gas is on, the filter's clean, the vents are clear, and one reset didn't do it, you're likely looking at a worn igniter, a dirty flame sensor, or a pressure-switch issue. All common, all quick for a technician — and none of them are homeowner jobs.
Before you call, run the free troubleshooter. It records what you ruled out and gives you a summary to read to the dispatcher, so the tech shows up ready.
Related symptoms
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