When it's fifteen degrees outside and your furnace won't start, it's easy to assume the worst. But a good share of the no-heat calls we run in St. Charles and across the Fox Valley come down to something small. Before you call anyone, spend five minutes on the following checks — you may save yourself a service fee.
1. Check the thermostat. It sounds obvious, but make sure it's set to HEAT and that the target temperature is above the current room temperature. If it's a battery-powered thermostat, replace the batteries — a dying thermostat battery is one of the most common no-heat causes we see, and a blank or dim display is the giveaway.
2. Check the furnace switch and the breaker. There's usually a switch that looks like a light switch on or near the furnace itself. It gets flipped off by accident more often than you'd think, especially in basements where people are moving things around. Also check your electrical panel for a tripped breaker.
3. Make sure the front panel is fully seated. Furnaces have a safety switch that cuts power when the blower door is off. If someone changed the filter recently and didn't seat the panel all the way, the furnace will not run at all. Push it firmly into place and listen for the click.
4. Look at your filter. A filter packed with dust restricts airflow badly enough that the furnace overheats and shuts itself down on the high-limit switch. If your filter is grey and matted, replace it and give the system twenty minutes to reset. In a house with pets, filters can load up in under a month.
5. Check the condensate drain. High-efficiency furnaces produce water, and that water drains through a small line and often a float switch. If the line clogs, the switch shuts the furnace off to prevent an overflow. Standing water near the base of the furnace is the sign.
When to call us. If all of that checks out and the furnace still won't fire, the likely causes are the ignitor, the flame sensor, the pressure switch, or the control board — all of which need a technician with the right tools. The same goes for any of these warning signs: a burning smell that doesn't clear, a furnace that lights and then shuts off after a few seconds, repeated short cycling, or a carbon monoxide detector going off. In that last case, leave the house first and call from outside.
A note about ignitors. Hot surface ignitors are a wear item — they're a piece of silicon carbide that glows red hot every time your furnace starts, and they typically last three to seven years. They almost always fail on the coldest night of the year because that's when the furnace is cycling most. It's a common, affordable repair, and we carry them on the truck.
PMV Heating and Cooling handles no-heat calls across St. Charles, Geneva, Batavia, Elgin, and the surrounding suburbs. Call (630) 415-8030 — we're open Monday through Saturday, 8 AM to 5 PM, with 24-hour emergency service available.