FAQ – the most frequently asked questions about heating

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How often does the heating system need to be serviced? Does Viessmann take care of maintenance of the heating system? What should you do if you get an error message? Here you will find answers and useful information to the most frequently asked questions about your heating system and heating in general.

1. Heating season and temperature

This aspect relates primarily to the relationship between tenant and landlord. The summer months are not part of the actual heating period. However, since this is not governed by law, the question of whether or not heating is required depends on several things, including the outside temperature. If the temperature turns too cold in the apartment or house and does not increase for several days, the heating will need to be switched back on again. As a homeowner, you can decide when the heating should be on or off.

A comfortable temperature is something that is very individual – some people need it a little warmer, whereas others do better with cooler temperatures. Nevertheless, there are some guideline values for the optimal room temperature for orientation. These are as follows for different parts of the home:

  • 20 to 22 degrees Celsius in the living room
  • 16 to 18 degrees Celsius in the bedroom
  • 18 degrees Celsius in the hallway and kitchen
  • 22 degrees Celsius in the children's room
  • 23 to 24 degrees Celsius in the bathroom

There is no legally prescribed point in time from which landlords must provide heat and generally speaking, heating periods are not defined in law. Nevertheless, the period between June to August has become firmly established as the typical heating period. As such, June is considered to be the starting point in many places. However, outdoor temperatures and minimum room temperatures play a much more central role than the date.

There is no generally valid ideal flow temperature. The ideal flow temperature depends on many factors, such as the energy condition of the building as well as of the heating system itself, the type and size of the heating surfaces and the type of heating system installed. The flow temperature should therefore match the house and the heating behaviour of its occupants. After all, excessively high flow temperatures cause high heating costs. If the flow temperature is too low, it will remain uncomfortably cool in the house. It is best to seek advice from a Viessmann trade partner, who can not only determine the correct values for hydronic balancing, but can also help you to set the optimum flow temperature.

2. Maintenance and repairs

Regular maintenance and thus appropriate care not only helps to maintain the functional and operational reliability of your heating system, but also its value. The burner, boiler and control unit should be inspected once a year. Regular inspection and maintenance will extend the service life of your heating system and ensure its safe and efficient operation. This will mean that the energy used is used as effectively as possible and as cleanly as possible. This helps to protect the environment and save heating costs. 

A heating system runs at full load for three to five months of the year. Therefore, heating system maintenance should be carried out regularly. This way, you can be certain that it will work properly for a long time. However, there are no legal regulations in this regard. In practice, a cycle of twelve months has become established practice for most types of heating system. An annual inspection is therefore recommended. In addition, you can also conclude a maintenance contract. That way, you will never have to worry about having your heating system serviced.

Heating system servicing is carried out by our qualified and appropriately certified trade partners. If you would like to order a service for your Viessmann heating system, contact the installer who installed your heating system. 

Hydronic balancing should be carried out if heat distribution in the home is very uneven. Without this, some radiators will remain completely cold, while others will become much too warm. Hydronic balancing is also recommended whenever individual heating components have been replaced or modernisation measures have been carried out. The energy demand of a home changes when modernisation is carried out. In addition, hydronic balancing may also be compulsory under certain circumstances, such as when you are applying for a subsidy.

Hydronic balancing should not be carried out as a precaution, but only if there is a need for it – i.e. heat is being distributed very unevenly in the home and some rooms remain cold. Accordingly, the following applies: hydronic balancing should only be carried out once. It only needs to be carried out again if something has changed in the heating system itself, such as the replacement of individual components. Repeated balancing is also advisable during modernisation projects. This is because energy efficient modernisation always result in a change in energy demand. The system can be adapted to the changes with the help of hydronic balancing.

It is not advisable to carry out hydronic balancing yourself as it involves optimising the heating system as precisely as possible, which requires all manner of calculations. Calculators provided free of charge offer only indicative values and should only serve as a guide. They are not a substitute for hydronic balancing by a heating contractor.

A heating system check determines the optimisation and savings potential of a heating system. To do this, a heating contractor will thoroughly examine the heating system and uncover weak points that reduce energy efficiency. The result is a qualitative energy assessment of the heating system in the form of a report. When a heating system check needs to be carried out is not prescribed by law. Nor is there any need to out checks at regular intervals. It is more about where there is room for improvement. At best, you should have your heating system checked in summer or autumn. There is then enough time to complete the necessary measures before the start of the next heating period.

If there is air in a sealed heating system, the heat can only be distributed with difficulty and the radiators will only be warm on one side. Similarly, it is not uncommon to hear noises such as knocking or whistling when you switch on the heating. If this is the case, the radiator should be vented. This allows the excess air to escape from the system.

3. Faults and damage

If there is damage to the heating system as a result of a thunderstorm or lightning strike, all live components must be replaced in case of doubt. An expert will need to carry out an assessment. Neither Viessmann itself nor the heating contractor can act as an expert. The costs that will be covered will depend on the insurance contract that you have in place. Depending on the case in question, the contract may be a contents, buildings or natural hazards insurance policy.

Viessmann control technology complies with the regulations and standards for interference immunity. In addition, the use of lightning conductors or lightning current arresters may also be useful. The individual units themselves are also equipped with fine protection. With this, the interference factors are directly discharged via a protective earth conductor.

Thunderstorms can also cause water damage and particular caution is required around the heating system electronics. Under certain circumstances, this damage can even lead to a fire. Therefore, it is recommended that all damaged components be replaced. An assessment of the damage and whether the costs will be covered will need to be clarified by an expert. Viessmann and its trade partners are unable to act as experts. You will need to consult the respective insurance contract that you have in place.

Viessmann offers a database query for operating instructions to help you with this. To use this feature, you will need either the serial number, which you will find on the type plate on the heating system, or the product name including the approximate date of purchase. If neither of these proves successful, you still have the option of requesting the instructions online.

You will find the serial number on the device itself. There will be a barcode sticker with a 16-digit number. If you are unable to locate this sticker, you can also ask your Viessmann heating contractor. The year of manufacture can be found on the type plate of the boiler or in report from the flue gas inspector. If you would like to know how old your Viessmann heating system is, the 16-digit number can help you – just look at the eighth digit.

If you have to bleed the heating system constantly, it may be that the system pressure is too low. You can read off the water pressure of a heating system on the pressure gauge. The green range on the pressure gauge is the optimum water pressure. If the water pressure is too low, you may need to add water.

In addition, the expansion vessel may also be faulty, in which case there will be a negative pressure and air will be drawn into the system constantly. In either case, it is best to consult an installer.

Our guide explains in detail how to find the right heating contractor.

You may find that there is a burner fault on your boiler. The fault codes may vary, depending on the model. The causes of faults are similarly varied. Please refer to the operating instructions for information on what to do in individual cases. We have compiled some general tips for you on the topic of faults

4. Function and technology

A heating system should run in summer mode during the warmer months of the year. This is both efficient and, if your boiler provides heating water as well as domestic hot water, ensures domestic hot water heating. Modern models also allow you to set room and outside limit temperatures. This way you ensure that the system starts up on cooler days in spring or summer, but not on every cool morning.

In order to save energy, it can make sense to switch off domestic hot water heating during the summer holiday period. If you have a decentralised domestic hot water heating system, this is simple and usually pays off, particularly if it is a rather small storage facility. However, larger cylinders with a capacity of between 250 and 300 litres should only be completely shut off when you are not likely to be at home for several weeks. This is because heating up a cooled-down cylinder of this size consumes a lot of energy, among other things.

There are a number of reasons why a system owner might need to top up the water in a Viessmann heating system. A heating water pressure that is too low may be an indication of this. Other signs include radiators remaining cold or annoying noises possibly caused by trapped air bubbles.

There are a few things to bear in mind when it comes to tipping up a heating system correctly. In addition to the instructions in the operating instructions, pay particular attention to the water quality. The heating water should comply with both the Drinking Water Ordinance [Germany] and the VDI Guideline 2035 in order to avoid damage to the system due to contamination and deposits.

The following steps must be followed:

  1. Connect the heating system to the water mains with a suitable hose. The special filling valve on Viessmann heating systems ensures that no heating water can flow into the DHW network.
  2. Make sure that the hose is filled to the overflow to prevent too much air from entering the system.
  3. The valves on the fitting and on the water inlet must be fully opened.
  4. The heating water must be topped up until the system pressure rises to about 1.5 bar.
  5. Close the valves again and bleed the radiators.

If in doubt, contact one of our Viessmann trade partners.

The hydrogen for cold combustion in a fuel cell heating system comes from natural gas. This consists to a large extent of methane, which in turn is composed of carbon and hydrogen. A reformer is needed to separate these two elements from one other – in the process, hydrogen and carbon dioxide are produced by means of water vapour.

It is advisable to replace a boiler after 15 to 20 years at the latest. This is because outdated heating technology consumes a comparatively large amount of energy, especially if the models are gas or oil heating systems without condensing technology. New models increase efficiency, reduce fuel use and lower heating costs. Modernisation can provide added security.

The heating contractor who installs the heating system will show you how the heating system works after the work has been completed. In addition to demonstrating the correct operation, they will also give you instructions on what to do in the event of fault messages or what to consider when setting the heating curve.

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