New cab;e colours

That's presumably a flex? The extra colour could be a switched circuit - but there's no real standard for this. And if it is a flex, these colours aren't new, but some 30 years old. ;-)

Most basic programmers require a line, neutral and two switch circuits (heating and hot water) but usually not an earth - although if it's mounted on a metal backing box that should be earthed. Please don't use the green/yellow for anything other than earth.

TLC sell 5 core flex (including an earth) by the metre for just this purpose:-

Yes, that's correct.

So if it is a switched live, it will need a red sleeve on it then.

Though the timer has a metal back box, when the timer body is connected to it, no metal can be touched, but the earth is good for when the timer is removed. I wouldn't use the earth core for anything but earth. :-)

The timer has 3 cables (flex) going into it. First is AC mains feed, the second and third go into the boiler and one these looks like going to the central heating shut off valve.

I am using 5 Amp flex for 2 of the cables and the new to me 4 core to carry the extra core.

Many thanks for your post

Dave

I have already 'plumbed in' 3 cables to connect to the timer

If flex, brown would be correct. Best not to mix standards.

Oh s*it. I forgot! Can I buy brown sleaving?

Dave

then.

Use brown insulating tape

AWEM

The same place that once sold red will now sell brown.

I dunno if the sheds sell short overpriced lengths like they do with green/yellow, though.

My brain must be more dead than I thought :-(

Many thanks to you and Andrew for pointing out the obvious.

Dave

I'm good at that.

I'm very glad you are :-)

Dave