iRT bus modification


Because additional reverse engineering of the iRT bus has shown that a modified EMS board is not the best solution, I have stopped selling the iRT modifed boards. A new design specifically for the iRT bus is being worked on. If you really want the iRT modified EMS board though, send me an email and I will still make one for you.


Old boilers like the Nefit Ecomline don’t use the EMS bus but the iRT bus. The EMS interface board can be modified to work with the iRT bus. I also sell modified versions in the webshop.

Victor-Mo reverse engineered large parts of the iRT protocol and adapted the EMS-ESP firmware to work with iRT.


The firmware and hardware modification is experimental. It may not work on your boiler. It may also need additional testing on your side. It is NOT plug and play. I cannot provide support.

Supported boilers

Boilers with the iRT bus are f.i. the Nefit Ecomline, Buderus GB112 and other boilers with an UBA 1.0 / UBA 4000 and UBA 1.5 / UBA 4001.

old UBA models


To interface with the iRT bus you need a modified EMS interface board. I sell these in the webshop. You also need a Wemos D1 Mini with the iRT firmware on it.

iRT modified board

The EMS interface is of course created for interfacing with the EMS bus. To make it work for iRT, SMD resistor R5 needs to be removed and a 1,5MOhm resistor needs to be placed on R21 or R22. If you buy the iRT modified board these modifications are already done.

iRT modified board

R22 (for through hole resistors) is placed in parallel with R21 in case you need to change the 1,5MOhm resistance.

If you ever want to revert back to EMS, you can remove R21/R22 and place a 100kOhm resistor on either R5 or R23. R23 is in parallel with R5.

iRT modified board

Wemos D1 Mini

As a microcontroller you have to use an ESP8266-based Wemos D1 Mini. Get the original one from Lolin, some clones have issues.

The iRT firmware

The iRT firmware is based on EMS-ESP 1.9.5.

To upload the firmware it’s probably the easiest to download the bin file from Victor-Mo’s Github repository 1 and use the NodeMCU method described HERE.

Operating modes

There are two operating modes, passive mode and active mode. In passive mode the firmware can decode the water temperature, if the boiler is running, what mode: heating or warm water, and if the pump is running.

In the (very experimental) active mode it will start the burner and sets a max water temp. The burner power is a fixed value depended on the water temperature you set, ‘set_water 35’ will set a maximum water temperature of 35 degrees Celsius and a very low burner power. ‘set_water 90’ will run the boiler at full power and a maximum water temperature of 90 degrees Celsius. For active mode you need to remove the thermostat because iRT does not support more than one device on the bus.

You can find more information on Victor-Mo’s Github repository 1.