Even the most reliable heating system can be faulty

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A heating system that's on the blink – this event often stays in your memory longer than all the other days on which it quietly does its job. We love convenience and quickly get used to comfortable room temperatures. So it's all the more of an unpleasant surprise when the heating system fails and that cosy heat does not materialise. To ensure that system users are not completely unprepared in the event of a heating system failure, we have listed the most important causes and measures in our guide, with which faults can be remedied quickly and safely.

Signs that the heating system is broken

A faulty heating system is usually noticeable by the fact that the radiators remain cold, despite the heating being switched on and the thermostats turned up. The following list shows which signs of heating faults occur:

  • one or more radiators remain cold
  • heating system cannot be started
  • heating cannot be switched off
  • heating system that is switched on keeps shutting down
  • heating system displays fault code/fault message

Causes of a faulty heating system

A heating failure can have various causes. The problem: most causes have the same effects to begin with, or at least similar ones: cold radiators and cold rooms. When confronted with this for the first time, it is often difficult to ascertain whether it is just an easy-to-fix everyday problem or whether there are serious reasons that may make it necessary to replace the entire system. Making this distinction is the first step.

Failures or malfunctions caused by operating errors, incorrect settings or lack of attention. If the heating simply does not get warm, the first thing to do is to check obvious causes: is there enough fuel? If so, is the fuel supply working? To check whether fuel needs to be topped up, a quick glance at the level indicator (for oil heating systems) is usually enough. To ensure the fuel supply, the corresponding components, for example the gas valve, should be checked. If the problem cannot be found here either, it is worth taking a close look at the connections. But this is only to provide information to the heating system installer.

Cause Solution  
Fuel has run out or is not being fed correctly Check level indicator, fill tanks/cylinders if necessary  
The heating curve is set incorrectly Reset heating curve  
Heating is still running in summer mode Change setting to winter mode  
Insufficient water pressure in the heating system Check pressure gauge, ideally: 1.5–2 bar, have heating water topped up, have hydronic balancing carried out if necessary  
Emergency switch has interrupted the power supply Press the emergency switch in the boiler room again and start up the system  
Fault message/fault code on the boiler Troubleshooting, find the code in the operating instructions, call a heating engineer  

The general rule is: a contractor should be consulted if causes are not clearly identifiable,. This applies all the more if individual components are faulty, for example the heating pump. In addition to the heating or circulation pump, thermostatic valves on the radiator can also be faulty. There are also many other components that may be defective, incorrectly adjusted or contaminated. These include, for example:

  • burner
  • overflow valve
  • oil filter
  • temperature controller
  • boiler sensor
  • heating control unit
  • expansion vessel

Should one or more of these components be faulty, expert skills are required. System users should immediately contact their trusted heating contractor to carry out a repair or replacement.

Inform contractor in advance about the fault code

Certain faults lead to a fault code appearing on the display of Viessmann heating systems. This is listed in a table in the service instructions for your Viessmann heating system. If in doubt, or if you do not have the service instructions to hand, it is best to ask the heating installer who installed your system. So the engineer can repair the heating system, it is advisable to note down the fault code displayed. Tell them about it on the phone at the next opportunity. This will help them prepare for the repair.

Does the boiler indicate a fault? Read our guide to find out what to do in this case

Heating failed? Keep warm with these tips

Once the heating engineer has agreed to attend, you must cope during the – hopefully short – waiting time. This is not always easy, especially when the temperatures outside are below zero. If the rooms at home remain cold, even a cosy activity like reading can turn into an ordeal. With our helpful tips, you can find out how to bridge the time until your appointment with the heating engineer despite uncomfortable room temperatures.
You can find out more about the benefits of a heating system maintenance contract in our guide "Heating system maintenance and maintenance contract".

Almost every household has a hot water bottle somewhere. If the heating system is faulty, a hot water bottle to snuggle with under your favourite blanket provides quick and reliable relief from feeling cold. It can be just as helpful to resort to grain pillows and, for those who have them, electric blankets. Of course, we should not forget the classic strategy for keeping warm: hot drinks.

People who don't move around and are also thinly dressed get cold more quickly than those who stay active even when at home for longer periods of time, for example by doing a few household chores. Putting on a jumper, thicker tights and thicker socks almost goes without saying in the event of a heating system failure.

Perhaps the most sensible tip on how to overcome the waiting period is to arrange a maintenance contract. To ensure that the heating system runs smoothly in the future, it should be serviced regularly. Most heating contractors offer a maintenance contract for this purpose

Anyone working in the kitchen during a heating failure benefits from several advantages at once: firstly, it helps pass the annoying waiting time, secondly, there will be something delicious to enjoy at the end, and thirdly – the main thing – the heat from the oven will keep the kitchen comfortably warm.

Candles not only provide a pleasant atmosphere, but also give off warmth to the room. However, the more candles you light, the more oxygen is consumed and the more combustion gases are produced. Candle lovers must decide for themselves whether it is worth having to let cold but fresh air in more frequently if their heating system fails. Lit candles should also never be left unattended and should always be placed on a safe surface.

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