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Heat won't turn on - what to do: how to diagnose & fix "no heat" problems in buildings. This article describes what to do if you can't get your building heat to turn on.
We give a simple sequence of steps in the order that is most likely to succeed, starting right at the wall or room thermostat and continuing through making sure there is electrical power and fuel. For more complex no-heat problem diagnosis we link to in-depth articles on heating boiler, warm air furnace, heat pump and electric heat repair procedures.
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On an older analog dial type thermostat you can't determine if the thermostat is working just by looking.
But turning the thermostat UP well above room temperature should turn the heating system on. Thermostats are usually powered by a low-voltage system wired from a transformer near or right on the heater.
If the thermostat has no power, check that its wires are connected, intact and that power is turned on at the heating system since power off there will often also turn off the transformer that powers the thermostat. Then
See FAN AUTO ON THERMOSTAT SWITCH for details about what turns the blower fan on and off on forced warm air heating systems or on air conditioning systems.
Separately, a FAN LIMIT SWITCH, we describe how this additional control, located on the heating furnace itself, should turn the forced warm air heating blower on or off. Don't bother with that switch yet.
Watch out: on some heating or cooling thermostats like the one shown at left, the device is so simple that the meaning of the temperature shown in the display may confuse you.
Left untouched and in HEAT mode, and controlling just a hot water heating boiler in this installation, the 67 degrees shown on the thermostat is the present room temperature.
So we cannot tell the SET temperature of this thermostat just by walking up and taking a look. So we don't know if the thermostat should be calling for heat or not, nor if it has been SET above the present room temperature.
Luckily and without even reading the instructions (a last resort for many of us) it's easy enough to figure out what's going on.,
The heating boiler was not running - I'd already checked that, and I'd also noticed that the radiators in the building were tepid or cool.
Just pressing either the "down" button (blue arrow pointing down in the photo above) or the "up" button (red arrow pointing up in both photos) will change the display to show me the present SET temperature.
Notice that the SET temperature is all the way down to 56 degrees? This thermostat has been told "don't turn on the heat until temperature in this room drops below 54F! No wonder the heat was not running. The room was already much warmer than that.
What if the thermostat doesn't turn on the heating (or cooling) system?
Now if I press the "up" button repeatedly until the SET temperature is well above 67F then the heat should turn on. It did.
If the thermostat does not cause the heating (or cooling) system to run when it should, there could be any of a number of problems (as we outline here) but among them you may need to check the thermostat itself or its wiring - starting
Watch out: to avoid embarrassment, don't forget to check electrical power switches including service switches that someone may have set OFF. For example
If you are confident that the no-heat problem is not due to electrical power having been turned off and not due to a thermostat not properly set, then you'll want to choose a no-heat diagnostic procedure depending on the type of heating system your building uses - listed just below.
Continue reading at one of the articles listed just below depending on the type of heating systerm your buildnig uses, or select a topic from the More Reading links shown below.
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