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Originally Posted by Ali
Hi,
My old Honeywell room thermostat needs changing. I bought a Horstmann HRT2. The old wiring was twin and earth style with the earth cut off (not used) and just the live and neutral cables being wired in. The instructions for the new thermostat indicates that 3 wires are needed: L - Common supply, Load - Call for Heat, N - Neutral. Can I use the existing wiring and just omit one of the connections ? If so, which one ?
Cheers....
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Some thermostats require a neutral to power the preheater which advances the switching of the stat to reduce short cylcing. As long as the stat still makes and breaks contact you can get away with not supplying the neutral. All you are doing is disabling the preheat element.
For most heating control systems you only need a contact which is made on call for heat. Establish which pin does this by placing a contiunuity tester on the common, and turning the dial up until you hear it click so as to call for heat. See which other terminal is "made". Double check by turning it down to see that the contact becomes broken.