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The heating system in summer mode

Photo: © Mila Supinskaya Glashchenko /

A heating system in summer mode saves energy and costs

Switch off the heating system in summer or leave it on? A valid question, as heating rooms is not usually necessary at summer temperatures. If domestic hot water is heated via the central heating system, however, this would result in a loss of comfort. If you switch off the heating in summer, only cold water will come out of the shower head and tap. In this case, it is recommended to set the heating system to summer mode. The heat generator then only runs to produce domestic hot water. This saves energy and reduces heating costs at the same time. In the following guide, you will discover what to bear in mind when changing over the heating system in summer and what alternatives there are for DHW heating.

This is why the heating system summer mode makes sense

Heating rooms and ensuring a supply of domestic hot water requires energy. The price for this is reflected in the fuel costs. The more energy is consumed, the higher these costs. Particularly in the case of fossil fuels, high energy demand is also associated with emissions. This is because CO2 is released when gas and oil are burned. If you set your conventional heating system to summer mode, you can not only save costs, but also reduce CO2 emissions. As the summer months are warm anyway, this is not even associated with less comfort.

The timing depends on the weather

There is no general rule as to when you should switch the heating system to summer mode. The weather conditions are the most important factor. However, the usual  heating season  in tenancies is a good starting point. It begins on the first of October and ends on 30th April. Accordingly, early May is a good time to check whether the limited operation of the heating system is sufficient.

Modern heating systems offer a lot of comfort

Those who already have a modern heating system usually do not have to worry about when to switch it over to summer mode. They automatically stop heating once a certain outdoor or indoor temperature is reached. This threshold temperature depends on whether heating system control is weather-compensated or room temperature-dependent. Accordingly, the sensors are installed outside or inside the building. If the temperature falls below a certain threshold, the heating system starts automatically. This ensures a high level of living comfort at all times, even during cold periods in summer. The temperature at which heating operation is stopped or resumed can be set manually. Refer to the operating instructions to discover how to adjust the so-called heating limit temperature on your Viessmann heating system and set it to summer mode. The operating instructions also describe how to set different operating modes:

  • Heating and DHW
  • Heating only
  • DHW only

The operating instructions are also available for download at Viessmann ViBooks.

Holidays offer great savings potential

The heating system should not only be turned down in summer. When you are not at home for a longer period, time programs also help to save energy. By activating the holiday program on your Viessmann heating system, you can influence both room heating and DHW heating. This is determined by the saved days of arrival and departure.

Setting older boilers into summer mode

Older boilers are still in use in many households. Since these usually do not have the corresponding control technology, energy saving heating in summer involves a little more effort. The boilers must be switched off or turned down manually. They are switched on again during longer periods of cold weather. You can make additional savings by switching off the heating circuit pump in summer. This is responsible for the water circulation in the radiators. However, to prevent the component also known as the circulating pump from seizing during the summer break, it should be switched on at certain intervals. With modern heating systems, this is done automatically. To avoid damage to the system and to find the optimum setting, it is advisable to consult a heating contractor. Your installer is a reliable contact when it comes to summer operation of an old heating system.

Tips for heating in summer

If your Viessmann heating system is running in summer mode, you are already saving energy and costs. In order to be well prepared for the next heating season and to make use of additional savings potential, we have summarised further tips on the topic of heating in summer.

Do not forget the thermostatic valves

Even if the radiators do not get warm during summer operation, the thermostatic head should not be set to frost protection. Otherwise, blockages can occur during the heating pause. This risk can be reduced by opening up the thermostatic valves on the radiators in summer. This releases the mechanism that regulates the flow of water in the valve. If the valves jam even though you the thermostats are adjusted correctly, you can try to free them up them yourself. To do this, first remove the controller cap. Once the lower part of the valve is exposed, tap it gently or pull lightly on the valve pin.       

Time switch for the DHW circulation pump

A DHW circulation pump ensures that all tapping points in the house are quickly supplied with hot water. This enables a high level of comfort. In addition, the constant movement reduces the risk of legionella formation. These multiply particularly well in warm, stagnant water. If this pump runs continuously, however, it permanently consumes electricity when no hot water is actually needed –– for example at night or when no one is at home during the day. In contrast to the circulation pump of the heating system, it should nevertheless not be switched off completely in summer. To save electricity, it is advisable to control the DHW circulation pump with a timer. In this way, the operating time can be adapted to the actual demand.

Using the summer for heating system modernisation

The summer months are the ideal time for a new heating system. This is because occupiers do not have to be cold even if heating is temporarily not possible or only possible to a limited extent. If the old boiler does not have a modern control unit, it is worth replacing the heating system. This eliminates the need to manually set the heating system to summer mode. In addition, innovative heating systems make particularly efficient use of the energy consumed. Those who opt for heat generators using renewable energy when modernising also conserve valuable resources and make themselves less dependent on fossil fuels and possible price increases. The modernisation of heating systems on the basis of renewable energies is also interesting because of government subsidies. These can significantly reduce investment costs for home owners. You can discover which heating systems are suitable for a heating system renewal in the following guides:

  • Alternatives to gas heating
  • Alternatives to oil heating

Solar thermal systems provide hot water in summer

If your heating system is running in summer mode, it only heats domestic hot water. With a solar thermal system, you can also produce hot water in summer without using the heating system and thus save even more. Proper planning is particularly important here. In order to make optimal use of solar energy, certain conditions must be met. Among other things, the orientation of the roof and its size as well as shading play are important factors. The required storage cylinder should also be matched to individual demand and the function of the solar thermal system. This is because in addition to DHW heating, the technology can also be used for central heating backup. A reliable contact for the planning of solar thermal systems is an experienced solar technician. They will adapt the new system optimally to the conditions on site.

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