OpenTherm --> Analog Converter

Forum about Opentherm, Hvac, House heating, Boilers

Moderator: hvxl

OpenTherm --> Analog Converter

Postby EPK » Tue Oct 25, 2016 1:47 pm

I have a Vaillant Aqua Plus (VUI 280-7) boiler that has an analog interface (pins 7-8-9) for flame modulation, so it expects a DC voltage range.
I would like to install a Honeywell Evohome system in my house that has an OpenTherm interface for flame modulation.
The boiler is still in a good shape, so no reason to replace it yet with a more modern one that has an OpenTherm interface, but instead it would be great if I could find an OpenTherm --> Analog converter that can be applied to my boiler.

Can anybody help me in this regards?
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Re: OpenTherm --> Analog Converter

Postby hvxl » Sat Nov 05, 2016 3:24 pm

I don't expect such a device is possible. In the Opentherm protocol, a thermostat tells the boiler how hard to heat by specifying a desired water temperature, rather than a straight percentage or something like that. Probably your analog interface just wants a voltage with a direct relationship of how high the flame should be.

In addition, an Opentherm thermostat needs a bunch of information from the boiler to determine the desired water temperature. The analog interface of your boiler doesn't provide that information.
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