Hello everyone, I wanted to share my recent experience integrating my new Nest thermostat with my Viessmann Vitodens 100-W combi boiler using OpenTherm. Initially, I encountered an error (H73) indicating that OpenTherm wasn’t detected. After some research and troubleshooting, I discovered that the installation guide specifies a maximum voltage of 42V DC for the OT1 and OT2 wires, but it doesn’t mention a minimum voltage. My boiler was supplying only 2.8 volts, which was below the required threshold for the Nest system to function properly on OpenTherm.
I decided to bypass the OpenTherm setup temporarily and wired the boiler using 230V switching, which worked seamlessly. However, my goal was to utilize the Nest’s OpenTherm functionality for more precise control. After some further investigation, I found that increasing the voltage to meet the minimum requirement resolved the issue. Now, my Nest thermostat is fully integrated with OpenTherm, providing efficient and accurate temperature control.
This experience taught me the importance of checking voltage specifications thoroughly and not assuming that the default settings will work without adjustments. I hope this helps anyone else facing similar challenges with their Nest thermostat and OpenTherm setup!