replace the old thermostat

[golannave]

Good evening.

I am trying to replace and old mechanical thermostat with a new
wireless digital thermostat. At the moment the system is controlled by
Honeywell ST6400C Programmer,

The old thermostat is Honeywell T6360

http://europe.hbc.honeywell.com/products/pdf/en0r8281uk07r1204.pdf

The wiring to the old thermostat is
3=N
1=L
And one goes to the Earth

I am trying to replace the old thermostat with SALUS RT500RF

http://www.heatingcontrolsonline.co.uk/instructions/RT500 RF MANU...

The problem is that I can't understand the wiring diagram; also there
is no option to earth in the new thermostat

I tried to connect only the L and the N but the problem is even when
the thermostat suppose to stop the heating it is still keeping it on,
the light on the receiver goes off but the electrical connection is
not been disconnected

HELP ....

Thank you

 

[D_Hailsham]

Are you sure that the Earth wire connected to the Honeywell T6360 is actually being used as an earth?. If you look at the wiring diagram at the URL you gave, you will see that this model does not require an earth. It does require three wires to work properly:Live (from time switch) - Neutral - Switched live back to Boiler/Motorized valve. The problem is that many "cowboy" installers can't be bothered to use the correct three core cable so they use twin and earth but make the earth the switched live.

Am I right in thinking that you will be retaining the Honeywell ST6400C Programmer. The wire from Terminal 4 (CH ON) should be removed completely as the Salus will control both time and temperature

The Salus wiring diagram is confusing; but here goes. The receiver needs three wires but no earth. The three wires do the same job as in the T6360, i.e Live - Neutral - Switched live. These are connected to the L; N and SL (On) terminals. The other end will connect to the same terminals as the old thermostat. If you cannot replace this cable with the proper 3 core (usually plus earth) and you are lumbered with the existing 2core + earth, the best thing to do is use the brown/red as Live, Blue/Black as Neutral and the earth as the Switched Live but put some black sleeving or insulating tape round the bare wire at both ends to show that it is a switched live. Not the best way, but it's preferable to getting a shock