I've seen a few references in various posts regarding a so called x-plan, but any links associated with the conversations lead to 404 errors. Can anyone point me to an explanation or diagram?
X-Plan
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Basically the CH 2-port is Normally Open and the DHW valve Normally Closed.
When there is a Priority DHW demand the CH valve is closed and DHW opens, so all flow is to the cylinder.
With Intergas boilers, typically a short circuited DHW NTC sensor is then connected, switching the boiler to a DHW lower power and higher flow temperature setting.
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Thanks for those. Makes for interesting reading.
One thing I'm still struggling to get my head around is why you need to have the CH 2-port normally open. Is it not more accurate to say that you want it closed whenever the DHW is called for? What am I missing?
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ok. I had assumed that if you were using OpenTherm then evoHome would simply open the CH / DHW valves as appropriate, and if you had enabled DHW priority that it would then always close the CH valve when heating the DHW. Obviously this is not the case.
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Sure, if you are happy with the same max flow temperature and boiler settings for both DHW and CH.
In my weather compensation setup, I disconnect the outside temperature sensor on DHW heating, detect it via OpenTherm Gateway firmware and boost the flow temperature to 70C, whereas for UFH CH, max flow temperature is 50C - Outside Temperature, reduced further by Evohome.
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Ok so this is where my complete lack of knowledge of OpenTherm (and perhaps naivety about evohome) shows. I had assumed, probably wrongly, that if you were using OT with evohome, then evohome would boost the max flow temperature if DHW was being call for.
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Originally posted by lloyd View PostOk so this is where my complete lack of knowledge of OpenTherm (and perhaps naivety about evohome) shows. I had assumed, probably wrongly, that if you were using OT with evohome, then evohome would boost the max flow temperature if DHW was being call for.
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I use this x-plan setup. My heat-only viessman boiler will not produce the high flow temps needed to heat a DHW cylinder unless its "DHW demand" terminal has voltage applied. without that , the flow temp is in the 50's.
So, the evohome HW BDR is wired to open the DHW zone valve. The end-terminal of the DHW zone valve is wired to close the (normally open) CH zone valve and activate the DHW demand mode on the boiler giving 79C flow. Result = 79C water going only to the cylinder. downside is heating circuit has no flow for the reheat time so timing is key.
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