I am trying to install an Elektra Model # MTC-3991 remote sensor thermostat on a two-wire 24 volt system. The thermostat is control a circulating pump on an econar geosource dualtek heat pump.

The old thermostat sensor is contained in the thermostat housing (mercury switch) reading air temperature. The replacement thermostat will read return line (cold) temperature.

On a air source heat pump what is the maxium length one can use for the sensor wire, which is supplied by the supplier at 5m. Which is in most cases to short to connect to and existing electric cylinder. Can one join the cable to extend the length.