Originally posted by paulockenden
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There is nothing in the OpenTherm spec to even make the boiler aware that a system might be zoned. What does zoned mean anyway ? Does a system with manual TRV's count as a "zoned" system ? Of course. Every zone can independently control the flow of water through it's radiator(s).
How many heat demands are sent to an OpenTherm boiler if you have a traditional single-zone thermostat ? One.
How many heat demands are sent to an OpenTherm boiler if you have a multi-zone system like Evohome, where individual zones can call for heat, and the demand is aggregated ? Still One.
The spec doesn't allow for communication of multiple zone heat demands, and even if it did, what would the boiler do with that information ? A boiler can only output one flow temperature on the heating circuit at a time.
In short, it's a nonsense excuse from Intergas for a problem that can't exist. Clearly there is some sort of issue with their OpenTherm support but it's nothing to do with not being able to handle a multi-zone system like Evohome.
bruce_miranda's suggestion may be closest to the truth - if Intergas is one of the boilers that can't limit the maximum flow temperature in OpenTherm mode and you have a complex schedule where there are frequently rooms increasing their set points it could well lead to a situation where the flow temperature is very high a lot of the time, where it wouldn't be on a single zone system, making it semi-useless.
However if this is the real issue, Intergas are certainly not alone, and it's getting to the point where Honeywell need to act and provide a maximum OpenTherm flow temperature setting in the Evotouch software. (Where you would expose it in the user interface I'm not sure though, as it would need to be a bit more prominent than being hidden in the installer menu, as mere mortals would need to be able to adjust it as the seasons changed...)
Has anyone here actually used Intergas OpenTherm with Evohome and if so what are the symptoms you notice (if any) ?
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