Written by Mascha

Help me determine which boiler I have

Don't know for sure whether your central heating boiler is on/off or modulating? We will help you find the right answer. How? By answering the questions below.

Identify boiler type

There are different ways to find out if you have an on/off or modulating central heating boiler. Below, you will find an explanation of what you should do per option.

Based on the serial number of your boiler

The most reliable way to find out what type of boiler you have is by taking the booklets from the boiler. That is because it exactly states the boiler's serial number and perhaps even what type of boiler it is. In addition, you can almost assume that when you have a new boiler in your house, it will have a modulating effect. It is mainly the old boiler variants that only have an on/off function.

Based on your current thermostat

Based on your current thermostat, you can find out what type of boiler you have. It is often stated on the thermostat whether it is modulating. Is that not the case? Then you can easily find out the type number via internet (usually at the back of the thermostat) and what kind of thermostat it is. Are you sure after a little research that you have a modulating thermostat on the wall? Then you can assume that your boiler also has a modulating effect. Unfortunately, this method of research is not the most reliable method. It can just be the case that you have been controlling the central heating boiler with a modulating effect for many years with an on/off thermostat.

Note: an on/off thermostat fits all types of central heating boilers. A modulating thermostat, on the other hand, is not. It really only works on modulating central heating boilers.


  • A central heating boiler with a modulating function is energy efficient.
  • On/off thermostats fit on every type of central heating boiler, but does not control a modulating central heating boiler.
  • Look at your current thermostat to find out what type of boiler you have.
  • Take the booklets from your boiler so that you can find out in the most reliable way what type of boiler you have.

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