Troubleshooting & how-to · August 2026 · HVAC Iowa City

Furnace won't start? The first three things to check

A silent furnace on a cold Iowa City night is frightening, and frightened people make expensive decisions. So before you call anyone, including us, take five calm minutes and check three things. A real share of the no-heat calls we take in January end with one of these, at a cost of zero dollars.

First, the thermostat. Confirm it's set to heat and the set temperature is above the current room temperature. If the display is blank or faded, change the batteries. Households share thermostats, and settings change without anyone remembering doing it.

Second, the furnace switch and the breaker. Near the furnace, usually on the wall or a ceiling joist, there's a switch that looks exactly like a light switch. It gets bumped by laundry baskets, storage boxes, and elbows more often than anyone would guess. Make sure it's on, then check the electrical panel for a tripped breaker. While you're there, confirm the furnace door panel is seated properly. Many furnaces refuse to run with the panel ajar, on purpose.

Third, the filter. A suffocating filter can overheat a furnace until its safety switches shut it down, which reads as "furnace is dead" but is really "furnace protected itself." If the filter is gray and packed, change it, wait a few minutes, and see if the furnace tries again.

If those three don't wake it, look through the small sight glass on the furnace cabinet for a blinking status light. You don't need to decode it. Just count the blink pattern and tell us when you call, because that code often turns a diagnostic visit into a targeted one.

Now the rule that outranks the whole checklist: if you smell gas, stop. Don't flip switches, don't relight anything, don't troubleshoot. Get everyone out of the house and call the gas utility's emergency line from outside. Gas safety is not a homeowner project, and no checklist on the internet, including this one, should tell you otherwise.

No smell, no luck, still cold? That's what we're for. Call, tell us what you checked, and we'll tell you honestly whether it can wait until morning and what it'll cost in writing before any work starts. In an Iowa City winter, no heat gets treated like the urgent thing it is.