Replacing Central Heating timer/programmer

[Boff]

Hi I have a very old SWITCHMASTER 400 timer and I'm looking to replace it with an electronic programmer.

It's a 24 hour mechanical timer with an Off/Timed/Constant switch and Water/Heating & Water switch.

I want to change it for a 7 day electronic one and also to be able to control the water and heating independently if possible.

I've seen a CentaurPlus C27 on TLC http://www.tlc-direct.co.uk/Technical/DataSheets/Horstmann/C11.htm which ticks all the boxes but I'm not sure if my current wiring will allow me to do this.

The terminals on the back of the timer are N L 1 2 3 4 with 1 being CH On, 3 being HW On and 4 is CH Off. 2 is blank.

Apart from Live, Neutral and Earth only 1 and 3 are wired.


Firstly, am I able to direclt replace it with the CentaurPlus C27 - WITHOUT ADDITIONAL WIRING?
Secondly, why is terminal 4 not wired? Is this what a 'Single Circuit System' is?

If I can't use the C27 would the C17 do?

Sorry for all the questions but the more info I'm reading the more confused I'm getting!

Cheers
Boff

 

[bster]

terminal 4 on the switchmaster is HW off in my manual.



I replaced my switchmaster with a C21 (same as C27 but only a 1 day programmer) so you should have no problems.

 

[Boff]

Ok cheers for that I'll give it a go and see how I get on then.

As for terminal 4, I'm pretty sure it said CH Off on the panel and I checked the manual for the newer Switchmaster 400 on the net and that said CH Off too. Doesn't really matter I suppose, it isn't wired anyway.

Boff

 

[bster]

You may have already seen this but just in case ....

http://www.horstmann.co.uk/downloads/ElectronicDocuments/Central-Heating/WiringGuide.pdf


look for ACL-Drayton switchmaster 400 (page 6?)

 

[Boff]

Cheers for that. It def says 4 is CH Off btw.

So I'd just run 1 --> 4 and 3 --> 3 then, looking at that. And I can just leave 4 (2 on the C21/27) out then as it is now.

One way to find out I suppose! Off to TLC tomorrow then.

Thanks again

 

[bster]

good luck and make sure that youve got a 3 amp fuse on the supply to the central heating system wiring .

 

[Boff]

The way it's wired at the moment, there are two sets of wires going to L & N.

One set is coming from a 13 Amp plug (haven't opened it up to double check) and the other is going down to the boiler along with the wires from 1 & 3.

So do I need to make sure the plug has a 3 amp fuse in it or do I have my wires crossed? (No pun intended!)

 

[Boff]

Well so far, so good.

It's all fitted and the timers are set.
They've both kicked in at the appropriate time and my rads are nice and warm so fingers crossed!

Thanks again for your help Bster!