Vaillant boilers and OpenTherm
Vaillant does not support OpenTherm directly out of the box in the UK. In a few european countries, such as the Netherlands, OpenTherm is highly prevalent and used, such that most boilers supplied have an OpenTherm interface or an adaptor to allow control. If you have come directly to this page, we maintain an OpenTherm capable boilers page at OpenTherm Capable Boilers and Controls
In the UK to use OpenTherm with a Vaillant boiler, you require a module called the VR33 module. It is produced by Vaillant primarily for the Netherlands. It is however not officially supported in the UK. We have installed it ourselves on previous jobs with success. A word of warning, Vaillant’s stance on this is that is will invalidate your warranty for using equipment not intended for the UK market.
Manufacturer’s Part No: 0020017895
Where to buy:
Vaillant has other brands in Europe that also use the same electronics. AWB is one such boiler that uses the same PCB or similar, therefore the OpenTherm adapter would likely be compatible. The part number for the equivalent is AWB OPENTHERM MODULE EBUS 0020092426. This module works out cheaper than the Vaillant equivalent at approx 56 EUROS
If you are looking for the module for Glowworm type of boilers, then it is AWB OPENTHERM MODULE 0020036768. This adaptor works out at approx 62.50 EUROS
Nest Thermostat 3rd Generation
We have successfully set up a system to operate a Nest Thermostat 3rd Generation using OpenTherm interface to control the Vaillant boiler via the VR33 module.
We have successfully used Honeywell Evohome with a Vaillant system boiler using a R8870 evohome interface connected to a VR33 module to operate the Vaillant boiler in OpenTherm modulating configuration. In this setup, external hot water also works at a basic level. We have been informed by other OpenTherm pros that, although this setup works, OpenTherm may not respond as well as it should, as compared with boilers containing built in OpenTherm interfaces.
Whilst the VR33 works to convert OpenTherm to Ebus, different manufacturer’s OpenTherm controls may yield slightly different results due to implementing subset’s of the OpenTherm protocol. Generally the biggest manufacturer’s such as Honeywell , Nest , Drayton etc tend to be closer to the correct implementation.