Opentherm Gateway for the win

Opentherm Gateway for the win

At the end of last year the central heating system (including hot water) at home started to fail. Luckily it was not directly broken, but it slowly gave less and less heat, which was most noticeable while taking a shower, brrr.
I was not totally unhappy then the maintenance guy told me the pump and three way valve replacement would be very expensive and besides that, the heating unit was nearing it’s expected lifetime. This way it was legit to buy a new one! One that could integrate with the already present home automation solution provided by openHAB.

It took a few hours to learn and decide which system was best for me. I won’t go into much detail about my selection and why, but I eventually came up with the Remeha Tezerra Plus 39c CW5 including Remeha iSense v28 thermostat. The heating system and thermostat are using the OpenTherm protocol to communicate. In the research process I learned there’s a device called the Opentherm Gateway which is capable of monitoring the OpenTherm messages that are passed between the heating unit and the thermostat, but most important, it’s able to set or override the setpoint temperature.

According to the compatibility matrix on the Opentherm Gateway website, this setup should work. So I ordered the USB version of the opentherm gateway kit at Kiwi electronics. This is a kit containing a pcb, components, USB cable and instructions. It took me a couple of hours to complete the soldering task, but now I have a working Opentherm Gateway, whohoo!

[![soldered otgw in the closet](](
Sorry for the poor image quality (phone, shaky hand and low light)
More than a week has passed since I soldered all loose pieces together and connected the gateway to the openHAB system by using USB. On the openHAB system, which runs raspbian wheezy on a raspberry pi 2, I configured the otmonitor-ahf program to run in the background as a daemon. This little nifty program also created by the creator of the Opentherm gateway, supports various methods of publishing it’s data. Lucky for me it also supports [MQTT]( I use this lightweight messaging protocol as much as possible, so it was easy to point it at the already running a [Mosquitto]( broker, which openHAB is subscribed to.
[![Screenshot from 2016-01-07 22:39:17](](
My current heating view, simple but efficient for other household members
Once it’s in openHAB I’ve set up some rules to set the temperature when my alarmclock goes off, coming home and leaving the house. Just need to add some graphs to monitor the times the heating is active and when hot water is used. Besides setting the setpoint temperature I also set the outside temperature. This can be displayed on the thermostat and the outside temperature is also used by the heating unit when using certain heating strategies. Don’t like to admit, but I will have to read the manual for that 🙂

Conclusion up till now: extremely satisfied with the chosen setup!