OpenTherm Compatible Boilers and Controls

Listed below are OpenTherm capable and compatible manufacturers and boilers. These boilers have integrated OpenTherm unless specified otherwise in brackets. For more information on OpenTherm, visit the OpenTherm Association. For homeowners wondering what OpenTherm means, see our guide on Modulating Boilers with Smart Controls.

What is OpenTherm?

Wikipedia definition: OpenTherm (OT) is a standard communications protocol used in central heating systems for the communication between a central heating boiler and a thermostatic controller. A two-way communications interface, usually in the form of a slave and master device. As a standard, OpenTherm is independent of any single manufacturer.

A controller from manufacturer A can in principle be used to control a boiler from manufacturer B. However, OpenTherm controllers and boilers do not always work properly together. The OpenTherm standard comprises a number of optional features and some devices may include manufacturer-specific features. The presence or absence of such features may impair compatibility with other OpenTherm devices.

OpenTherm History

OpenTherm was originally created by Honeywell and was sold to the OpenTherm Association on November 1996 for one British Pound. This was done to make the standard independent of any manufacturer.

Modulating Control

Unlike room thermostats that simply tell the boiler when to turn on and off (non-modulating), a modulating control tells the boiler the exact target/setpoint temperature that is required to be achieved. As the current temperature starts getting closer to the set point temperature, the boiler starts reducing the flow temperature to match the required demand.

This results in:

• Higher efficiency through better condensing operation
• More comfortable temperatures with less overshoot
• Reduced cycling and wear on components
• Lower energy consumption

OpenTherm Advanced Setups

OpenTherm is easier to use on combi boilers, as there is no hot water cylinder to control. Stored hot water requires heating to the correct temperatures as required by legionella prevention (recommended 60 degrees). Since OpenTherm can reduce flow temperatures below 60 degrees, on system and regular boilers with stored hot water, cylinder temperature reporting must be present in some form.

This allows the OpenTherm system to fire at high temperature just for the hot water. In this setup, it is advised that there is priority to the hot water system, otherwise higher temperatures may reach the radiators when you don't want them to.

OpenTherm Compatible Boilers

The following boilers have native OpenTherm support. Some Vaillant Ecotec 4XX series models require additional configuration steps - see Vaillant OpenTherm Guide for details.

Unofficially OpenTherm Compatible Boilers

The following boiler models are capable of OpenTherm using unofficial adaptors. These are mostly Vaillant and Worcester Bosch models. Using the mentioned adaptors may invalidate your warranty on new boilers, but for boilers that are out of warranty there are no known problems. These adaptors are purpose-made by the manufacturers for some European countries where governments have made OpenTherm compulsory.

OpenTherm Compatible Controls

The following are OpenTherm compatible heating controls and smart thermostats. These controls are compatible with OpenTherm capable boilers shown above. For homeowners wondering what OpenTherm means, see the OpenTherm Association fact sheet.

Last Updated: 25/09/2022

Summary

This comprehensive list covers the majority of OpenTherm compatible boilers and controls available in the UK market. OpenTherm provides significant benefits in terms of efficiency and comfort when properly implemented.

For brand-specific OpenTherm implementation guides:

• Vaillant OpenTherm Guide - Including VR33 module installation
• Worcester Bosch OpenTherm Guide - EMS to OpenTherm adaptor information