Spent the day working through Failure Modes and Effects Analysis (FMEA) of our ASHP system. I have hit on one which has me wondering if I have missed something.
When the ASHP goes to heat the Domestic Hot Water (DHW) it provides a voltage to the changeover valve in the house that switches the ASHP flow from the Under Floor Heating (UFH) circuit to the DHW heating circuit. All well and good except that there is no feedback to the ASHP, that I can spot, that confirms the valve has actually moved and the the circulation is now running round the DHW circuit. In the situation where it fails to change over we will get the much hotter water, normally reserved for heating the DHW, flowing into our UFH which as a strict upper limit on the floor surface because of the floor coverings. There is a temperature probe feeding the DHW cylinder temperature back to the ASHP but the lag on that could be significant even supposing the ASHP has a mechanism for detecting that there is no rise in temperature of the DHW despite it apparently delivering 55oC water to the cylinder. This seems like an oversight to me, have I missed something or am I expected to provide an external solution - any thoughts or observations?