Posted 17 October 2023

Thermostat boiler modulation

I have a system boiler (Vaillant) which is controlled by Nest but this seems to be just be on/off and doesnt take advantage of the modulation possible. Some further research and i've gotten into the world of Ebus/Opentherm.

Does anyone have a Vaillant System boiler and which thermostats are you using to achieve modulation?
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  1. themorgatron's avatar
    You can buy an Opentherm module for vaillants, they're over £100 though.

    Your likely problem will be the boiler cant differentiate between a call for heat or call for hot water. You only want the opentherm adjusting the flow temperature when in heating mode, not hot water.

    Vaillants work best with their own controllers.
    samosa's avatar
    Author
    Thanks, that’s the conclusion I’m drawing up. Some say tado thermostats will do ebus but only for combis. I’ve got an engineer coming out this week so will look at the various possibilities.
  2. TheUrbis's avatar
    I believe the later Nest stats support OpenTherm?
    samosa's avatar
    Author
    Thats correct but Vaillant use Ebus. I've found the majority will support Opentherm but hardly anything out there for Ebus.