Home Assistant contains a component to control an OpenTherm Gateway, but it seemed not very stable. The gateway sometimes has timeouts and these also happen in Home Assistant. The problem was that HA stopped in the middle of the night and became unresponsive. To resolve this problem I have created a go program that copies temperatures from and to the gateway. This is a lot more stable as the timeouts don't hinder the processing. With a input_select component and a few automations I now have a more stable and responsive heating control system.