CENTRAL HEATING PROGRAMMER WIRING

[mngray]

Grateful for some advice on changing my CH programmer.. Current programmer is some kind of Venner (precise spec unknown - it has a rotating clock dial with two "on" settings and two "off" settings as well as two three-poisition switches - HW and CH constant, timed and off). New programmer I am installing is a Horstmann C27. New programmer has standard 6 terminals: N, L, 1, 2, 3 and 4. Old Venner timer has 8 terminals: N, L, 1, 2, 3, 4, A/S and one next to A/S. I have 4 wires coming in: boiler, pump, mains and wire from thermostat. Current wiring is as follows:

Mains: live to L, neutral to N, earth to E.
Thermostat: live & neutral to A/S and one next to it, earth to E.
Pump: live to 3, neutral to 4, earth to E.
Boiler: live to 1, neutral to 2, earth to E.

I cannot quite see what is happening at the A/S area, i.e. which wire is going to which terminal, until I start undoing wires. However a blue wire comes back out of the A/S area and into the N. The N is the only terminal with 2 wires going in.

That is the current system. Question is how do I wire up the new programmer?

Thanks for your help.

Mark

 

[oilman]

Has the new programmer got wiring instructions with it?

 

[mngray]

Yes it does, but not quite so straightforward as it seems, because the wiring diagrams assume a seperate wire from a cylinder stat. I may have one, but I know that only a single 3 wire (E, L, N) connection comes in from elsewhere (i.e. is not the pump, the boiler or the mains).

What it also shows is a numer of ways of replacing Venner electro-mechanical timers. Unfortunately they are all different and clearly my old one does not have a model number on it! I cannot find any website telling you what the model might be. However only 2 of the listed models used all six terminals, so I assume it must be one of those two (Ventrol 80M or Ventrol 80P/M. The instructions say that the A/S connection goes to a "spare" and I'm not sure exactly what that means. The description says "If spare terminals have been used on the programmer being replaced then any connected wires should be removed and re-connected into a seperate piece of terminal block" - what exactly does that mean?

Any clues?

Mark

 

[breezer]

it means they are surplus to requirements