Wiring diagram for old central heating system

Hi,
The "diverter valve" has gone bang on my mum's central heating system and we are told that it is obsolete.
The system looks very much like a modern Y plan system - fully pumped, 3 port valve, separate timed control of heating and hot water, etc. The only difference from a modern Y plan system is that the wiring box contains a relay.
The plumber is being useless, so I may have to do the work myself, it should be a straightforward task to replace the "diverter valve" with a modern 3 position valve and replace the wiring centre with a modern one without the relay.
The tedious bit will be identifying all the unlabelled wires coming into the wiring centre - a task which would be made a lot simpler if I had a wiring diagram.
Does anyone recognise the description of the system and have a wiring diagram they could scan for me (or point me to one on the Internet). The system is of mid 70's vintage (1976 or 1977 I think) and the diverter valve and wiring centre are made by Satchwell. Unfortunately I am unable to see any part number on the diverter valve.
TIA, Martin.
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In an earlier contribution to this discussion,

Can't help with original wiring diagram, I'm afraid. But surely, there can't be *that* many wires? There should be wires going to: * Boiler * Pump * Programmer * Room stat * Cylinder stat * Diverter valve
Unless you're very unlucky, some of the cables will be different colours and/or sizes or number of conductors from the others - so if you see what they look like at the remote end, you can probably identify most of them at the wiring centre end. Failing that, you'll have to disconnect them at both ends, short live to neutral at the remote end of each one in turn, then use a continuity checker at the wiring centre end.
What you're aiming at when you re-connect everything is a standard Y-Plan setup as per http://content.honeywell.com/uk/homes/systems.htm (scroll down to Y-Plan). The only slight change to this would be if the boiler needs pump over-run - which is unlikely if it's 30 years old!
Things to watch are that the programmer must have a HW OFF connection and the cylinder stat must be the changeover type, with 2 connections. It's just possible that the existing ones don't - and that the relay does what they would otherwise have to do.
--
Cheers,
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Hi,
As a follow up to my previous post I have put a couple of pictures of the diverter valve on a webpage in case it helps jog anyone's memory.
http://www.wiseman999.plus.com/diverter.htm

That is true and I have some idea of how it is all connected up because I spent a very happy half term week at the age of 10 watching it all being installed, however I do recall that the "professional" who installed it wired everything up with multiple lengths of identical 3 core cable.
Hence all the cables from the boiler, programmer and room stat look identical at the point they enter the airing cupboard.
Working it out will be straightforward, however it would be much quicker and much less tedious with a wiring diagram.

I'm pretty sure it does. There are certainly more than 3 wires going to the boiler.

A good point, which hadn't occurred to me. Those are also things that a wiring diagram would help with (I should point out that I don't live particularly close to my mum so I can't just pop over there to have a look). What I am hoping is that I can just turn up on Sunday with a 3 port valve and wiring centre and wire it up so that at the bare minimum she has heat that she can manually switch on and off.
Martin.
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On Wed, 12 Oct 2005 21:55:44 +0100, Martin Wiseman wrote:

Quite a few of the wires will lead to nearby items. E.g. cylinder stat, pump. The incoming mains should be easy to identify. The boiler and pump may well be in parallel so easy to find.
The relay might simply be there because the programmer/timer does not provide and HW off signal.
The remaining wire(s) will be to a room and/or frost thermostats.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Martin Wiseman Wrote:

This is an old Satchwell system - now 'Sunvic Controls Ltd'. Th actuator is still made - part no DM5601, the valve body is an MK145 and you can still get a replacement circuit board and relay for th junction box part no RJ2801. Phone the Sunvic helpline on 0169881094 for more info and a wiring diagram. If you fit a standard 3 port sprin return valve you will need to replace the motor unit and the valve body
-- malcolm
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