Thermostat Not Working

A failed thermostat leaves working equipment sitting idle with nothing telling it to fire, so a call is the quickest way to find out which side quit.

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When this becomes an emergency

The display shows nothing at all, or only a low battery symbol.
The equipment runs whether the thermostat calls for heat or not.
There's a several-degree gap between what the stat reads and what the room feels like.
Nothing changed except a thermostat swap, and now a zone won't run.

What a pro does

Two things get separated first: does the thermostat have power, and is its signal reaching the equipment. Batteries and a tripped breaker on the control transformer cover a surprising share of dead displays. Beyond that, a technician jumpers the terminals at the equipment to see whether it fires without the thermostat in the picture at all, which settles the question quickly. Equipment that runs constantly usually means two wires touching somewhere in an old run, often where a wire was stapled tight during some past remodel and the insulation finally gave up. On a recent thermostat swap, wiring at the new stat gets checked against the old labels, because zone valve systems and simple furnace hookups don't share the same terminal conventions.

Frequently asked questions

What does it mean if the heat runs no matter the setting?

Usually a shorted thermostat wire or a stuck relay, both of which keep the equipment seeing a permanent call for heat regardless of what the thermostat is asking for.

The thermostat was just replaced and now a zone is dead. Why?

Terminal lettering isn't consistent across systems, and a wire that ran a zone valve on the old stat can end up on a terminal that does something else entirely on the new one.

Can a thermostat read the wrong temperature without being broken?

Easily. Sun on the wall, a draft from a stairwell, or a spot on a cold exterior wall all give readings that don't match how the room feels.

Do old mechanical thermostats need replacing?

Not automatically. A clean, level mercury or bimetal stat can hold a room well, and swapping one out won't fix a fault living in the wiring or the equipment below it.

Thermostat Not Working?

Get connected with a local pro now.

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