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Wiring in a new Thermostat THat Needs Moving Slightly

Postby akababa » Mon Nov 20, 2017 9:46 pm

I need to move a thermostat along the wall about 20cm to make space for some new storage and have decided to replace it with a new one. After having done a bit of googling I'd appreciate it if anyone could confirm:

What type of cable I need - the original is 3 core and earth (3 wire thermostat) but the earth is not connected (in one of my pictures you can see it poking out the sheath)

If I do need an earth where does it connect to on the thermostat

What type of connectors/junction box should I use to extend the cable (i.e. rating etc.)

I've attached pictures of the existing wiring.

Many thanks.
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Postby ericmark » Mon Nov 20, 2017 10:51 pm

The old thermostat uses neutral to reduce the hysteresis, with modern thermostats they are often battery powered and don't need the neutral, Regulations say with a fixed installation earth must be provided even if not required or used.

For a new build it says the thermostat since it needs you to manually adjust it should not be mounted higher than 1200 mm and because you need to read it, should not be mounted lower than 1200 mm so they are always mounted 1200 mm high.

Also we have safe zones, so to a device the cable can go vertical or horizontal but not both or diagonal. So to move a cable which drops down the wall 6 inches will mean removing the cable from the wall to ceiling height then moving sidewards and then back down to new location.

Also it clearly needs free air movement, where a thermostat is placed is very important, I bought a wireless thermostat which could be placed on a table, desk or other furniture, being so easy to move I tried in different locations. The results really surprised me. In the room 90 deg from radiator wall it was very poor, opposite wall far better, and on a table 2 foot away from radiator it needed setting to higher temperature but worked very well.

So you have all the cables needed to connect to a wireless hub. It does not matter where the hub is, once paired you will never touch it again, so you can mount it higher or lower to miss unit or even at the boiler.

The thermostat can then be mounted where there is free air flow.

You get what you pay for, Honeywell Y6630D Wireless Room Thermostat has anti hysteresis software built in and also protection should signal be lost, but is not programmable.

Horstmann HRFS1 Programmable Room Thermostat seems to offer so much more, but mine failed within 6 months losing the RF link making house either very cold or very hot.

So learn from my error, if getting wireless then get good quality.

Thermostats like Nest with the right boiler using OpenTherm will instead of switching on/off switch the boiler up/down giving far better control, best is likely EvoHome which will allow you to control each room independently. Using TRV electronic heads.

Wired it starts around £20 Flomasta 24701SX Wired Digital Thermostat seems pointless when Flomasta 22199SX Wired Digital Programmable Thermostat is only £24 and programmable, nothing wrong with wired cheap it is only the wireless cheap which is a problem. Or maybe I was just unlucky?
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Postby chriscba » Mon Nov 20, 2017 11:00 pm

If you are installing a standard 230V room stat they require a live, switched live and neutral, thats why you need a 3-core and cpc rather than just a 2-core. However, if you are installing a digital room stat they only require a 2-core and cpc.

Terminals on the stat are usually numbered 1,2,3 and 4. 1 is usually live feed in, 2 is usually neutral, 3 is usually switched live out and 4 you dont use. Plus you will have an earth terminal for your cpcs.

Cable size is normally 1.5mm2 heat resistant.

Remove the stat, make the connections & fit a blanking plate, then trunk across to the new position.

Be careful you connect the new the same as the old one, you could damage the boiler.

If in doubt contact an electrician
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Postby Mr White » Tue Nov 21, 2017 5:44 am

You need 3 core and earth (The same as what you have, its available in most DIY stores)

Any junction box needs to be accessible, so you could use a 4 way junction box and secure it to the wall, as it has its own integral lid nothing else would be required. (Just don't cover it with your wall unit.)

Alternatively you could use wago connectors and a wago box, these you could cover with your new wall unit.
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Postby akababa » Fri Nov 24, 2017 8:01 pm

Thanks for all the info. Think I'm gonna go for a wired thermostat. What amp does the junction box need to be?
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Postby Mr White » Fri Nov 24, 2017 10:28 pm

A 5 amp junction box will be fine. It must have 4 terminals (one for each wire) screwfix can supply them for a mere 69p

You can use a bigger rated one if you wish. (But it must have 4 terminals)

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