If you use the "orange wire" method as suggested then you must fit relays to the UFH systems to pick up if they are running and also to any zone valve with chopped off orange wires, if too short, one relay might do the wole lotl.
Re your own suggestion above, to prove/disprove it, connect a test light across one of those relays and ensure it stays lit during both normal boiler burner on and off. For pump overrun, observe it while you switch off the last heating circuit, the boiler circ pump should/might overrun and the relay test light should stay on until pump overrun complete.
Re your own suggestion above, to prove/disprove it, connect a test light across one of those relays and ensure it stays lit during both normal boiler burner on and off. For pump overrun, observe it while you switch off the last heating circuit, the boiler circ pump should/might overrun and the relay test light should stay on until pump overrun complete.
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