Scenario. Old two wire thermostat Honeywell (R and W wires), the R was hooked up to 24v transformer**, W connected to one of the yellow wires going to the motor on the zone valve, and the other yellow wire attached to the zone valve motor goes to the other side of the transformer**. For those that don't know, the circuit is open (no juice) until the room temp is lower than the thermostat setting. If so, the thermostat closes the circuit (connects the R and W wire allowing juice to flow. This in turn cause the valve motor to open (and when in the complete open position further closes another the circuit to the pump calling for it to turn on) - We have a Multizone system.
Bought a lyric T5 honeywell. Stated I needed a Common Wire for 24 volt power for the unit itself. Luckily I thought, I found a folded back third wire I could use as common. I attached this wire in the propane boiler room to a transformer thinking aha, 24v power. Apparently I was wrong just like the R and W loop (2 wires), I would need a fourth wire to complete a loop for power through the common wire???
Hence my dilemma.
Possible solution is perhaps tap off at the thermostat the 24v R wire and jump this to the C wire attached to the other side of the thermostat thus creating a live circuit. This would have no effect on the zone valve because the thermostat doesnt connect R and W until there is a call for heat (temp lower than thermostat setting).
Is this possible, safe credible, or am I hosed with 3 wires???
