"floating" voltage in central heating wiring

[MarkRainbow]

I recently replaced the syncron motor in a to port heating zone valve.

Before rplacing the motor thaat I had removed, I checked the voltage supply to it in the power up and power off conditions. I got the expected 240V in the power on condition, but when test ing the power off state, I found the voltage was about 115V. (Both measured to Earth as I didn't have a newutral I could easily connect to)

After I connected the replacement motor, the power off voltage dropped back close to zero, maybe 20V or so.

Could anyone give me any insight as to why I would be seeing this? A poor neutral or earth connectiion somewhere perhaps? Or is it nothing to worry about, just an induced voltage in an open ended wire somehow?

Thanks

 

[TicklyT]

Consider what is happening further along the circuit you are testing. Where do the wires you are testing run from and to? is that point connect via whatever heating control or input it is to a live or a neutral, or is it just floating until another control operates?

Modern high impedance multimeters are more prone to picking up stray induced voltages and capacitive coupling that would be safely shunted away by the coil of an older style analogue meter.