The heating does not get warm – what can you do?

Check the setting of your heating system:

• Is it still set to summer mode?
• Does the heating run exclusively on DHW heating?
• Is the system time set correctly?
• Has the system jumped back to the default setting after a power cut?

These settings can be read directly from the display of your Viessmann heating system. With most Viessmann systems, they can be changed via a mechanical controller or via the display's touchscreen. For older heating systems, it is highly recommended to call in an installer to avoid causing damage with the incorrect settings.

In this case, the heating engineer will probably have to free up a jammed thermostatic valve or replace the thermostat. Reason: the thermostat has been set to zero or the frost protection position has been unchanged for a long time in summer, so the valve has become jammed and no longer allows heating water to flow into the radiator.

The heating engineer has to bleed the radiator. Reason: there is air in the heating circuit. You may be able to bleed the radiator yourself. Our guide to bleeding the heating system explains how to do this and what equipment you need. However, a check is necessary afterwards and it is best to consult a contractor if you are in any doubt.

The heating engineer has to carry out hydronic balancing. Reason: the water in the heating circuit is not evenly distributed, so that the pressure ratios between individual radiators differ excessively. This can occur, for example, after replacing several radiators or renewing the boiler. The German Federal Office for Economic Affairs and Export Control (BAFA) subsidises hydronic balancing by 30  percent.

Reason: The heating circuit pump is not functioning properly. To check this, you can hold the tip of a screwdriver against the pump housing and listen for vibrations or flow noises at the handle of the screwdriver. If nothing can be heard, the heating circuit pump is not running. Notify your heating contractor of the problem; they will repair or replace the pump.

A fault in the boiler can have various causes. The heating system installer can determine the fault from the fault code that appears on the display of your Viessmann heating system. They then delete the code, make the necessary repairs and, in the best case, simply switch the boiler on again. It is best to have the code ready when you contact the contractor. Then they can be better prepared.

The reason for the failure is most likely a lack of fuel. Check the fuel supply to your heating system:

• Is the gas tap open or closed?
• What is the fill level of my oil or gas tank?
• Is the feeder in a pellet or wood chip heating system jammed or blocked?

Have a contractor check your heating oil system, your LPG tank or gas connection –– depending on which heating system you have in operation. Oil or gas tanks must never run completely empty. If the level indicators fall below the necessary filling level –– usually 15 to 20  centimetres for oil –– the burner is already getting too little fuel or no fuel at all.

If the entire heating system can no longer be started, this may be due to the emergency switch being pressed by mistake, for pellet heating systems, oil heating systems or wood chip heating systems. A small light on the emergency switch shows whether the switch is in the "on" or "off" position. Press the switch again and restart the boiler. If in doubt, consult your heating contractor.