Your lights dip for a split second every time the furnace starts, and a lot of people would describe it as SPOOKY!!
But, is it a problem?
A brief, slight dim is normal. A few versions of it aren’t, and since we work on both the furnace and the wiring, we see every one of them.
Motors take a big gulp when they start
The blower motor in your furnace pulls several times its normal running current in the first instant after it turns on. That surge drags the voltage down a little, and anything sharing the circuit, lights especially, dims for a fraction of a second. Your refrigerator and washing machine do the same thing.
LED bulbs tend to show it more than old incandescent bulbs did, so plenty of people first notice this right after swapping their bulbs out.
When it’s worth a call
- The dim lasts longer than a second, or it’s dramatic
- It happens across the whole house rather than in a room or two
- Lights ever get BRIGHTER instead of dimmer (that can point to a loose neutral connection, and it shouldn’t wait)
- The flicker comes with buzzing, an outlet cover that feels warm, or a breaker that trips
Sometimes it’s the furnace
A failing capacitor makes the blower motor struggle to get going, so the startup surge gets longer and deeper. The motor still runs, which is why this can go unnoticed for a long time. That’s exactly the kind of thing our furnace tune-up on our coupons page is meant to catch.
Sometimes it’s the house
Other times the wiring is the weak link. It might be a circuit carrying more than it should, a loose connection at the panel, or older electrical service that’s being asked to handle a lot more than it was built for. Plenty of Milwaukee’s older bungalows and duplexes were wired long before anybody owned a microwave, never mind a furnace with a variable-speed motor. That’s an electrical repair call.
Because we do both, one visit can usually tell you which side of the wall the problem lives on. Call us at 262-220-7020.
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