I'm currently looking at modifying the install of an S plan with CH Zone, HW Zone and single UFH zone off a vaillant combi. The wiring diagram is attached, mine are the wonky lines! The UFH diagram is partially complete but the missing wires are hopefully obvious. I have read that the UFH manifold pump is fed directly from the UFH thermostat as I have shown here which surprised me as I thought it would be fed by the valve switched live when open but now I see it makes little actual difference.
The only question I have is that this means in a situation where the UFH TRV does not need any hot water (UFH is running at correct temp) and is closed and the HW is off and the CH ZV is off (My CH will come on later in the morning) BUT the UFH thermostat IS demanding heat the boiler pump may well run which will force flow either through the internal boiler Auto by pass or an external fitted auto bypass. It seems from what I have read that this is OK? I thought the bypass was kind of for 'emergencies only' in case of some type of failure but here it may be used much more frequently. Can you advise on what bypass pressure should be set at on the external one please or how I can figure it out? Thanks.
The only question I have is that this means in a situation where the UFH TRV does not need any hot water (UFH is running at correct temp) and is closed and the HW is off and the CH ZV is off (My CH will come on later in the morning) BUT the UFH thermostat IS demanding heat the boiler pump may well run which will force flow either through the internal boiler Auto by pass or an external fitted auto bypass. It seems from what I have read that this is OK? I thought the bypass was kind of for 'emergencies only' in case of some type of failure but here it may be used much more frequently. Can you advise on what bypass pressure should be set at on the external one please or how I can figure it out? Thanks.