Changing a room thermostat
 

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....

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.

On Tue, 28 Dec 2004 13:33:32 +0000, Ali
strung together this:


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 ?

The old wiring is live and call, not live and neutral.

Connect up the live to the common suppy and the call to call. You can
omit the neutral connection, it helps to keep the temperature more
regulated, basically.

I would recommend you use a programmable room stat as these are more
accurate and will work with only the two wires that you have.
--

SJW
Please reply to group or use 'usenet' in email subject

The instructions for the new thermostat indicates that 3 wires
are needed: L - Common supply, Load - Call for Heat, N - Neutral.

The thermostat you have chosen is an old mechanical bimetallic type, whilst
your system is wired for a modern type. Although you can get it to work by
omitting the neutral, it will operate very poorly. Send it back and buy a 2
wire electronic type, preferably programmable.

Christian.