Are the heating elements functioning properly? To find out, remove some stones from the sauna heater and check if the heating elements warm up after switching the heater on. If a heating element does not turn red, it is damaged and needs to be replaced before further use of the heater.
Are the cables properly connected? Ask an electrician to disconnect the sauna heater from the power supply, and to verify that all cables of the heater and the controller are connected to the main module in accordance with the user manual of the sauna heater.
If this does not solve the problem, take a picture of the main module cabling and email it to us at with a description of the problem.