Thermostat won’t turn on: causes, solution.

Thermostat won’t turn on


  1. The batteries are out
  2. Energy saving mode
  3. If thermostat gets power from the power grid
  4. Dirty thermostat
  5. The fuse is broken

The batteries are out

If your thermostat gets power not from the power grid, but from the batteries, then you need to check them. It will be better to replace them with new ones.

Energy saving mode

Some models of modern thermostats have a power saving mode which can turn off the display by pushing one of the buttons while the functionality of the device will remain the same. Check if the display can be activated again by pushing one of the buttons.

If thermostat gets power from the power grid

First, you need to check if there is power in the supply terminals. To do this, turn the power off, remove the thermostat from the wiring box without disconnecting the wires. Then turn on the power and check the voltage in the thermostat supply terminals. If there is no voltage in the supply wires – the problem is not in the thermostat itself, but in the wiring or in the switchboard.

In certain types of thermostats, the correct connection of the Line and Null wires to its contacts is what causes malfunction. If your diagnostics revealed that the Line wire goes to the contact designed for the Null wire, then the thermostat won’t turn on and you will need to interchange the wires in order to restore correct phasing.

If the power is on, the phasing is correct, and the control indicator or the display of the thermostat do not turn on – the thermostat may have failed. This is a serious malfunction and sometimes it is easier to replace the entire thermostat.

Dirty thermostat

Like any other equipment, thermostat can suffer from dust. Small particles can negatively affect both mechanical and electrical parts. It can even cause a short circuit which can damage your thermostat or affect its operation. Open the thermostat and clean it.

The fuse is broken

Perhaps your model of thermostat is equipped with additional fuse which protects it from power surges. In order to check if this fuse has failed, simply open the thermostat and look for a glass flask on the control board which should have a thin metallic thread inside. If that you see no thread (it burns out and breaks off), then the fuse is out of service. It must be removed and replaced with exactly the same kind of fuse. We do not recommend putting a fuse or closing the contacts, since there is a high probability of the entire thermostat failure.