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Honeywell evohome and Your Boiler: Worcester Bosch, Vaillant, Baxi and More

Honeywell evohome controls a boiler in one of two ways. A Wireless Relay Box (BDR91) switches it on and off. An OpenTherm Bridge (R8810) talks OpenTherm to boilers that support it. Which one suits you depends on your boiler brand.

Sumcraft Editorial Team7 min read

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Honeywell evohome works with most UK boilers. It uses a BDR91 relay for on/off control, or an R8810 OpenTherm Bridge on boilers that support OpenTherm.

Checked on 4 November 2026. Everything below comes from Resideo's evohome installation guides and the boiler makers' own documents. They are linked at the end. Resideo makes Honeywell Home products. We have not installed evohome ourselves. Have a competent person wire anything at the boiler.

Boiler brandWhat the boiler maker saysevohome connection
Worcester BoschDoes "not use open therm on any of our range of boilers". Its own controls use EMSWireless Relay Box (BDR91), on/off
VaillantUses eBUS. Its VR33 module adds an OpenTherm connectionBDR91, on/off. OpenTherm only through a VR33 (ask Vaillant)
Glow-wormUses eBUS. We found no Glow-worm document mentioning OpenThermBDR91, on/off
BaxiCurrent Combi 2 and System 2 boilers are "Fully compatible with OpenTherm"OpenTherm Bridge (R8810), or BDR91
Ideal"Ideal Logic boilers have OpenTherm wiring connections"OpenTherm Bridge (R8810), or BDR91
ViessmannA boiler needs "a pre-installed OpenTherm interface". The Vitodens 111-W manual mentions an OpenTherm controlR8810 where the boiler has OpenTherm. Otherwise BDR91

Two ways evohome connects to a boiler

Wireless Relay Box (BDR91): on/off control

Resideo's installation guide says to "connect the Wireless Relay Box to your boiler's thermostat terminals". The relay switches the boiler on and off. The boiler then runs at the temperature set on its own controls.

Resideo's wiring notes for the relay:

  • Mount it "at least 30cm from your boiler", on a non-metal surface.
  • "Remove link at boiler if fitted." Some boilers have a link across the room thermostat terminals.
  • "If the boiler has an inbuilt timer leave this on constant."
  • Check the boiler's instructions to see whether it needs a permanent live supply.

OpenTherm Bridge (R8810): OpenTherm control

The R8810 lets evohome talk OpenTherm to "an OpenTherm boiler". Resideo is clear about where it goes: "Opentherm input on the boiler ONLY. Do not connect to the room thermostat terminals."

With OpenTherm, evohome can tell the boiler what water temperature to run at. Our guide Is my boiler OpenTherm? covers how to check your boiler.

Pairing the relay with the controller

Resideo's guide gives these steps to bind a BDR91 relay as the boiler controller:

  1. Make sure the relay is wired to the boiler and powered up.
  2. Press and hold the relay's button for 15 seconds, until the red light blinks quickly. This clears any old binding.
  3. Press and hold the button again for 5 seconds, until the red light blinks slowly.
  4. On the evohome controller, press the green bind button.
  5. Check for a SUCCESS message. If it does not appear, repeat the steps.

Resideo says a relay supplied in a Connected Pack is already bound as a boiler controller.

evohome with a Worcester Bosch boiler

Worcester Bosch said in 2020 that it does not use OpenTherm on any of its boilers. So evohome connects through the BDR91 relay to the boiler's 240-volt room thermostat connection. Worcester says third-party controls are fine "however the controls must be 240 volts".

Many older Greenstar boilers have a timer in the front panel. Resideo says to leave a built-in timer "on constant". Our Worcester guide covers Greenstar timers and Worcester's own controls.

evohome with a Vaillant or Glow-worm boiler

Vaillant and Glow-worm boilers use eBUS for their own controls. evohome does not speak eBUS, so it uses the BDR91 relay. Vaillant's ecoTEC pro manual says to connect a 230V control's switched live to "the RT marked X1 position".

Vaillant makes a VR33 module that connects "an OpenTherm third-party control" to a Vaillant eBUS boiler. Resideo's guide does not name Vaillant. Ask Vaillant whether a VR33 suits your boiler before you buy one. Our Vaillant guide and Glow-worm guide have more detail.

evohome with a Baxi, Ideal or Viessmann boiler

Baxi says its 400 Combi 2.1, 600 and 800 Combi 2 and 600 and 800 System 2 boilers are fully compatible with OpenTherm. Ideal says its Logic boilers have OpenTherm wiring connections. On these boilers, the R8810 OpenTherm Bridge is an option. The BDR91 relay also works for on/off control.

Viessmann says a boiler needs a pre-installed OpenTherm interface. Its Vitodens 111-W manual says to "remove the jumper across L and 1" when connecting an OpenTherm remote control. Ask Viessmann about your exact model.

Our Baxi, Ideal and Viessmann guides cover each brand.

Quick answers

Does Honeywell evohome work with a Worcester Bosch boiler?

  • Yes, as an on/off control through the BDR91 Wireless Relay Box. Worcester says none of its boilers use OpenTherm.

Does evohome work with a Vaillant boiler?

  • Yes, as an on/off control through the BDR91 relay. Vaillant boilers use eBUS, which evohome does not speak.

Does evohome support OpenTherm?

  • Yes, through the R8810 OpenTherm Bridge. Resideo says it connects to the boiler's OpenTherm input only.

Can I use any wireless thermostat with my Worcester boiler?

  • Worcester says third-party controls work if they are 240-volt controls. evohome's BDR91 relay connects that way.

How do I pair a BDR91 relay with evohome?

  • Hold the relay button for 15 seconds to clear it, then 5 seconds to enter binding. Then press the green bind button on the evohome controller.

Who should install evohome?

  • Resideo says devices that connect to mains electricity should be installed by a competent person.

Sources, checked 4 November 2026:

  • Smart thermostat
  • Honeywell evohome
  • OpenTherm
  • Boilers
  • Home heating

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