Hi,
>
> My old Honeywell room thermostat needs changing. I bought a Horstman
> HRT2. The old wiring was twin and earth style with the earth cut of
> (not used) and just the live and neutral cables being wired in. Th
> instructions for the new thermostat indicates that 3 wires are needed
> L - Common supply, Load - Call for Heat, N - Neutral. Can I use th
> existing wiring and just omit one of the connections ? If so, whic > one ? >
> Cheers....
Some thermostats require a neutral to power the preheater whic advances the switching of the stat to reduce short cylcing. As long a the stat still makes and breaks contact you can get away with no supplying the neutral. All you are doing is disabling the prehea element.
For most heating control systems you only need a contact which is mad on call for heat. Establish which pin does this by placing contiunuity tester on the common, and turning the dial up until yo hear it click so as to call for heat. See which other terminal i "made". Double check by turning it down to see that the contact become broken
-- Paul Barker