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Why is my furnace running but not producing heat?

What’s likely going on

A thermostat set incorrectly or with a dead battery is worth ruling out first — it's the simplest explanation. Beyond that, a dirty filter, a pilot light or ignition issue (gas furnaces), or a tripped safety switch are all common, genuine mechanical causes.

Is this a DIY job or worth calling someone?

Checking your thermostat settings and batteries costs nothing and rules out the simplest cause. Anything involving the furnace's gas or ignition components is a real job for a licensed technician — not something to open up and troubleshoot yourself.

Not sure, or ready to have someone take care of it?