Rewire Switchmaster 905

[michaelpoolman]

Hi I am trying to wire in a new digital central heating controller Im stumped


In my current setup Swithmaster 905 -I currently have connections going to the following


B – Yellow/Green Cables x3

N – Black / Blue / Blue

L – RED x1

CH ON – RED x1

HW ON – BROWN x1


I then have a black cable belonging to CH ON cable not being used and a spare brown cable (Don’t know where from) not being uses – Wired into C (Spare Terminals)

I have no CH OFF or HW OFF Wires - Its connected to a Rayburn it it helps

Currently the central heating and water is on all the time and controlled by the temprature dial

Im trying to wire it into a Honeywell ST9400C – can anyone help?

 

[D_Hailsham]

B – Yellow/Green Cables x3

Yellow/Green usually means an earth wire; but it's not unknown for heating engineers to use these wires to carry voltage. You need to check, the other ends of each wire to ensure they are earths.

N – Black / Blue / Blue
L – RED x1
CH ON – RED x1
HW ON – BROWN x1

That's normal and will connect to the equivalent terminals on your new programmer.

I then have a black cable belonging to CH ON cable not being used

How do you know it is not being used - can you see the other end is disconnected? If it is not being used, disconnect both ends and make safe with insulating tape.

and a spare brown cable (Don’t know where from) not being uses – Wired into C (Spare Terminals)

As above - find the other end a check it is not being used.

I have no CH OFF or HW OFF Wires

CH OFF is never used; HW OFF is only used if you have a 3-port valve.

Which model of Rayburn do you have and what fuel?

The ST9400C is a two channel programmer, so you can have different heating and hot water times, but the 905 uses the same times for both. This could be because you can have HW ON by itself (summer), but not have CH ON without HW ON (winter).

Do you have a fully pumped system or is the hot water on a gravity circuit

How many motorized valves and pumps do you have?

Currently the central heating and water is on all the time and controlled by the temperature dial

I assume you mean the temperature dial on the Rayburn and that you do not have a wall thermostat or hot water cylinder thermostat.

 

[michaelpoolman]

I understand i am on a gravity water and pumped central heating

The spare black cable from the wall temprature dial is connected to the dial itself just not the controller im not sure about the brown wire

what i call the spare back and brown was orginally wired into a spare terminal together

 

[D_Hailsham]

I understand i am on a gravity water and pumped central heating

Sounds like it. Definitely, if you have no motorized valves.

The only way you will be able to make use of the separate heating and HW times of your new programmer is by converting the system to a C Plan. This requires a motorized zone valve in the hot water circuit, a cylinder thermostat and a wiring centre.

The spare black cable from the wall temperature dial is connected to the dial itself just not the controller I'm not sure about the brown wire

Is this the temperature dial I asked about and never got a reply? Or is it another temperature dial?

So you have one black wire connected to this dial. Are there any others? If so where do they go?

Any chance of finding the other end of the brown wire?

what I call the spare back and brown was originally wired into a spare terminal together

I take it these are different wires to the two mentioned earlier.

Why were they disconnected from the spare terminal? Can you find the other ends.

Have you checked the yellow/green wires are earths?

 

[michaelpoolman]

The temprature dial is a honeywell in the hall way a oblong shape chrome colour? it had a red and black wire connected to it

Ill try and locate the brown wire when i return home tonight

Really i just wanted to change to a digital controller instead of the old one without changing parts am i able to do this?

Rayburn is standard gas

 

[D_Hailsham]

The temprature dial is a honeywell in the hall way a oblong shape chrome colour? it had a red and black wire connected to it

The red wire should be same wire as the one connected to CH ON of the Switchmaster. The black wire will probably go to the pump.

Ill try and locate the brown wire when i return home tonight

OK

Really i just wanted to change to a digital controller instead of the old one without changing parts am i able to do this?

You can do this. The Honeywell ST9400 will have to be configured as a Mini-programmer (see installation instructions). As you will have found out, the only way of controlling the hot water temperature is by the thermostat on the boiler. Converting to the C-plan (info on installation instructions) means the hot water temperature is independent of the boiler temperature.

 

[michaelpoolman]

does this mean if the two cables are not currently in use (brown & black) i can tape up or to they have to be earthed or goto neutral


In the current setup i have four cables in total wired into the controller as it does not have a control box

 

[D_Hailsham]

does this mean if the two cables are not currently in use (brown & black) i can tape up or to they have to be earthed or goto neutral

In the current setup i have four cables in total wired into the controller as it does not have a control box

Four cables, but how many wires in each cable?

You must find out what both ends of each wire is connected to before any one can say it is safe to disconnect and tape up.

Post a list of what you find.

 

[michaelpoolman]

The only two cables not in use is the Black cable (Temprature Dial in hall way) and a brown cable

In the orginal Wiring these two cable have been wired together in a unused socket (no power/functions what so ever)