Electronic Heating timer ( Honetywell ST 6400 C

[Soup]

I recently purchased a Honeywell programmer ST 6400 C to replace my old Randall 4033 anticipating that it would be relatively straight forward to change them over, how wrong was I !!!!!

Removing the backplate I exposed a series of wires that bared no resemblance to the wiring diagram with the new programmer. I have located the room thermostat wiring and the power supply but the two remaining am unsure which is the water and which the heating. The only thing to differentiate between them is that one has 4 wires ( earth, blue black and brown ) the other has 3 wires. Any clues ?

Would anybody have any idea how to wire it up to my existing central heating system with the existing wires of a room thermostat ( red and black), power supply ( earth, live, neutral ) heating connection ( ? ) and water connection ( ? ) ?

The new programmer has the following connections: -

Earth
N = Neutral
L = Live
1 = HW off
2 = CH off
3 = HW on
4 = CH on

If not I'll probably get an electrician in to do it.

Your help would be much appreciated.

 

[croydoncorgi]

Don't (necessarily) get an electrician to sort out heating wiring - many of them will be as confused by it as you are.

Chances are that one cable goes to the boiler (the 4-wire), the other to the pump - maybe.

You never said what sort of system you have - conventional, motorised valves, system boiler, ...?

Boiler wiring is quite logical - but only if you understand what you have and what each bit does.

If you don't want to climb the learning curve, get a heating engineer round. If the wiring is in good condition and the rest of the system works, it should not take more than 1 hour to change the backplates and wire-up.

 

[ollski]

4033 to st 6400c

6 to L
7 to N
E to n/a or any earth point
4 to 3
5 to 1
2 to 4
3 to 2

Don't forget prelim. electrical checks before you fire it up though

 

[Soup]

Ta very much ollski.

 

[croydoncorgi]

Huh???
No information was provided about the allocation of the wires in the wall.
Without knowing where the wires go, making the suggested connections is unlikely to be right and could short-out your nice new programmer!!

 

[Soup]

I haven't got round to it yet but i'll hold back now. I've got a slightly better idea but still am unsure which cable is which.

I refer everyone to my first question !!!

The system I think is a conventional one, a pump, boiler, etc. But don't know how to amalgamate the thermostat into the wiring. Obviously it will act as a switch to turn the water on or off ( I think !!! )

 

[croydoncorgi]

I'm afraid your username is where you'll end up if you do not find out what you're trying to wire up before you start connecting things!!
Where (for example) the thermostat goes depends on what's out there.

The absolutely basic problem is that I would expect to find 5 OR 6 connections on a back-plate (Live, Neutral, Earth, C/H on, H/W On, and maybe H/W off, depending on whether you have a three-port motorised valve or not). You appear to have 12. I guess what's happened is that someone has decided to do without a 'wiring centre' as such and has put the interconnections in behind the programmer. Did the Randall controller have a row of 'empty' connectors provided only to provide places to connect wires together rather than connections into the programmer itself?

Your new programmer does not include the extra terminals, so best thing to do is put a wiring centre immediately below the programmer. Honeywell offer a 10-terminal junction box specifically for this purpose.

 

[namsag]

Going from left to right on the 4033 terminal strip which has 8 connections


1 not used
2 heating on
3heating off
4hot water on
5 hot water off
6 live
7 neutral
8 earth

So whatever terminals the instructions say on the new honeywell clock match to these this is where they go

 

[Soup]

Just to let everyone know my wife actually mentioned if the heating controls may be covered under our house insurance, would you believe it they are !!!! I contacted our insurer and they sent a heating engineer round to wire it up !!

Not bad eh !!! Heating is working fine now.

Thanks to everyone for the comments of help.