Hi, I need a bit of help replacing an old Drayton RTS1 thermostat with a Honeywell T6. The Drayton has standard live, neutral and call cabling connected via relay, but the T6 expects two "Thermostat" wires and is 20V. This rules out connecting the 230V live connection. I believe the T6 receiver box will feed the 20V to the thermostat, but my problem is I only have the call wire. Will I need to install an additional wire? Has anyone had experience replacing this type of thermostat with a smart one?