Moving heating timer - Honeywell ST6200A


Postby armitageshanks » Tue Nov 04, 2008 9:13 am

Hi,
I would like to move a Honeywell ST6200a heating timer. It has a five wire mains connection consisting of the normal twin and earth cable, and another cable which I think is 3 core and earth, the wires from this are yellow, blue, red & earth.

Before buying the wire I want to check what core I should use and what size junction box.
I think its 2.5mm twin & earth and 2.5mm 3 core and earth.
I'm unsure of what size junction box to use.

If any one can advise that would be useful.

Many thanks,

Nigel
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Postby ericmark » Tue Nov 04, 2008 10:52 am

Most timers require 6 wires (including earth) but have 7 connections. These will normally come from mains supply and go to the room thermostat and tank thermostat often via a junction box.
The problem your likely to have is wires in walls. There are permitted zones and these are defined by where visible electric boxes are mounted so if you remove a switch, socket, timer, thermostat etc. You will also have to remove the cables.
As a result my old timer is still on the wall although set to 24/7 on as the thermostat now has a timer built in and instead of switching on and off it changes the temperature according to time of day.
Honeywell site now requires registration up to a few months ago it was open access but they produce a special junction box to join all the cables. But many builders have not used these and use a socket box with connector strip.
As a result tracing the wires of a central heating system can be a nightmare.
As to colour codes only the wires out of the motorised valve are set colours the interconnecting cables if your lucky may be numbered but more likely to be red, yellow and blue in any order.
I tried to help someone before and http://www.ericpalmer.fsnet.co.uk/Centr ... ating.html may also help you.
As to buying wire if it is to be buried then Ali-tube may be best as it does not require RCD protection but as to number of cores you will likely find any thing other than triple and earth expensive and hard to source in short lengths and using a role of triple and earth and running two cables where required may be only option.
As most central heating is supplied from a switched fused connection unit with a 5 amp fuse even 1mm cable will take this current.
I would think twice about moving it can be a nightmare. If you do be very careful taking notes of what goes where. I would suggest taking photos before you start to remove any cables so if you do make a mistake you have something to refer back to.
Except when using off peak power can’t see point in timer on hot water we lag our tanks now, and as I said Horstmann DRT2 thermostats and the like make timers on central heating redundant so if you don’t need to access does it still need moving?
Eric
ericmark

Postby armitageshanks » Tue Nov 04, 2008 11:18 am

Hi,
Thanks for this Eric. My access to the wires is fairly open as I have taken down the ceiling underneath our hot water supply.
The current timer has the 6 wires attached as described in the previous post, rather bizarrely, the earth wires from the 2 cables are joined together but do not enter the timer.
The heating system is an oil fired one and I know little about it, but the actual timer has been removed from the wall and is easier enough to rewire as I have moved it already based on the amount of existing spare cable I have that is attached to the timer.
The timer has separate settings for the heating and the water.
The rooms do not have individual thermostats and all of the heating is controlled by the timer and the radiator valves.
However it is not ideally positioned and I would like to move the timer around 2 metres from its current position.
It sounds like the 1mm 3core and earth would be okay with existing 2.5mm twin and earth. However is this a safe way to move it with junction boxes or do I need to rewire the whole thing?

Thanks for your advice.

Nigel
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Postby ericmark » Tue Nov 04, 2008 10:13 pm

They are not easy to rewire so if you can get away without all the better. You must have access to any junction box using screws there are specials using a spring clip arrangement that can be inaccessible.
As to use of timer I can see how with TRV's it makes sense I only have TRV's upstairs.
As far as electrics go very little between oil and gas except more gas boilers are variable output than oil. With variable output switching on and off can be a problem as the radiators have to be very well adjusted using the lock shield valves. Less important with on/off type.
There are different systems called C, Y etc but it is common to control the motorised valve which in turn controls the boiler and the domestic water thermostat can stop central heating from working which means fault finding can be really hard so note every wire very carefully.
Eric
ericmark

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