Worcester Bosch and OpenTherm

Worcester Bosch and OpenTherm

Worcester Bosch OpenTherm has eluded us here at MyBoiler.com for a while. New information has surfaced showing that it is indeed possible to use OpenTherm with a range of Worcester Bosch boilers using an adaptor. The boilers that operate using the modern EMS protocol system can be used with this adaptor to allow OpenTherm Thermostats to control Worcester Bosch boilers and other EMS protocol based boilers, although in the UK only Worcester Bosch is known to use some form of EMS.

If you have arrived directly at this page, you are able to see our main page on opentherm boilers and compatible controls at OpenTherm Capable Boilers and Controls

Nefit EMS-OT OpenTherm converter

Nefit OpenTherm Adaptor
Image: Nefit OpenTherm Adaptor


Description: This adaptor will take an OpenTherm capable thermostat and translate to the proprietery Worcester Bosch bus interface. It translates from OpenTherm to EMS

  • Manufacturer part no: 7 746 901 847
  • EAN: 4051516774516
Image: Wiring Example with Nest Thermostat to Nefit EMS-OT Opentherm Adaptor to Worcester Bosch Boiler
Image: Wiring Example with Nest Thermostat to Nefit EMS-OT Opentherm Adaptor to Worcester Bosch Boiler



Where to buy:


Nefit Moduline Easy Connect adapter for OpenTherm devices

Nefit Easy Connect
Nefit Easy Connect

Description: This adaptor allows the Worcester Wave or Nefit equivalent to connect to an OpenTherm interface.CV-Ketel is dutch for Boiler. This adaptor has now been superceded by the Nefit EasyControl adapter shown below.

  • Manufacturer part no: 7 746 901 787



Bosch / Nefit EasyControl adapter for On-Off, OpenTherm and iRT

Nefit Easycontrol
Bosch / Nefit Easycontrol


Description: This adaptor allows a Nefit or Worcester Wave thermostat to communicate to other boilers with On-Off, OpenTherm and iRT interfaces. Please note this adaptor only takes an EMS signal and outputs to On-Off, OT (OpenTherm) and iRT, not the other way round. It is not capable of allowing an OpenTherm thermostat to work with an EMS based boiler such Worcester Bosch

  • Manufacturer part no: 7 736 701 346 EU, 7 736 701 560 UK
  • EAN: 4057749327925


Bosch EasyControl Instruction Manual

Image: Example Wiring Diagram Worcester Wave / Nefit EasyControl OpenTherm Boiler
Image: Example Wiring Diagram Worcester Wave Bosch Nefit EasyControl OpenTherm Boiler



Functions and Features according to Opentherm.Eu

ID0:HB0: Master status: CH enable
ID0:HB1: Master status: DHW enable
ID0:LB0: Slave Status: Fault indication
ID0:LB1: Slave Status: CH mode
ID0:LB2: Slave Status: DHW mode
ID0:LB3: Slave Status: Flame status
ID0:LB6: Slave Status: Diagnostic/service indication
ID1: Control Setpoint i.e. CH water temperature Setpoint (°C)
ID3:HB0: Slave configuration: DHW present
ID3:HB1: Slave configuration: Control type
ID3:HB3: Slave configuration: DHW configuration
ID3:LB: Slave MemberID Code
ID5:HB0: Service request
ID5:HB2: Low water pressure
ID5:HB3: Gas/flame fault
ID5:HB5: Water over-temperature
ID15: Maximum boiler capacity (kW) / Minimum boiler modulation level(%)
ID17: Relative Modulation Level (%)
ID18: Water pressure in CH circuit (bar)
ID19: Water flow rate in DHW circuit. (litres/minute)
ID25: Boiler flow water temperature (°C)
ID26: DHW temperature (°C)
ID27: Outside temperature (°C)
ID28: Return water temperature (°C)
ID35: Boiler fan speed Setpoint and actual value
ID36: Electrical current through burner flame [µA]
ID48: DHW Setpoint upper & lower bounds for adjustment (°C)
ID49: Max CH water Setpoint upper & lower bounds for adjustment (°C)
ID56: DHW Setpoint (°C) (Remote parameter 1)
ID57: Max CH water Setpoint (°C) (Remote parameters 2)
ID115: OEM-specific diagnostic/service code
ID116: Number of succesful starts burner
ID119: Number of starts burner during DHW mode
ID120: Number of hours that burner is in operation (i.e. flame on)
ID123: Number of hours that burner is in operation during DHW mode


Other useful articles and links:

OpenTherm Gateway – http://otgw.tclcode.com/

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