Problem encountered replacing Back Box

Licklieder

Licklieder

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Been fitting new thermostats to my flat. In a couple of cases this means working round the old circular backboxes (some metal, some plastic but all mounted on conduit) with imperial screw fittings & in some cases said screw fittings in completely the wrong place.

Just dug out the wall round the next one i'm replacing in the bedroom, and having cut the old circular back box out, there's nothing there - just a hole in the wall to the next back box that needs replacing in the 2nd bedroom. Cabling runs from back box in room 1 to back box in room 2 as they're both on the same radial circuit.

My obvious problem is that there's nothing to mount a new steel back box to. If I can i'd like to use the existing void in the wall rather than cut out new ones.

I was wondering whether I could use that old fave expanding foam to fill the void and mount to that. Or hardwall for that matter.

any comments / suggestions ?

Matt
 
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thermostats?.. plural as in more than one?

same radial??? now you've lost me, each stat should surely have their own cable controling whatever valve etc that controls the heating..

a picture of the hole and the "stats" that you are replacing would help us greatly as I for one cannot picture the problem from your description..
 
Sorry, I've not been very clear.

Each room has its own thermostat inline with the electric heater for that room. There are three radial heating circuits from the CU, each rated at 16A :

1) Lounge
2) Kitchen & hallway
3) Bedrooms 1 & 2

I've elected to replace each of the original thermostats with 7day programmable versions, costs more but I'll get better control in each room.

I'll take a picture and upload it shortly
 
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If the wall is plasterboard and hollow try plastic dry-line box as already suggested.

If the wall is solid use expanding foam or bonding/undercoat plaster. Use metal box. Make sure box is level before it sets.
 
Backbox1.jpg
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Backbox2.jpg
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IF those remains of conduit boxes will pull off you can get some 20 mm bushes to fit on, and fix the boxes to these. This will help to hold the boxes in position.

Chances are the old fittings are glued on.
 
Thanks all.

you've given me something to work with and now I know what I'll be up to tomorrow.

I'll try taking the reamins of the boxes off, and then expanding foam I think - as its quicker setting than hardwall.
 
If that's the cabling to the stat, it looks like you've just got a live feed & return/switchwire.

In which case there's no neutral, which you'd need to feed your programmer.
 
Expanding foam isn't the right material. Use bonding and if you make it thick (and then work quickly) it will start to cure near immediately and will fully set in half a day.
 
D

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