FCU to electric towel rail - aaargh!

[Steviec9]

I hope someone can shed light on what may be a problem here - it's got me very confused.

Renovating bathroom - removed (working) wall fan heater fed by FCU outside bathroom (bathroom is next to kitchen - FCU is in the kitchen, load feed wire through wall directly into appliance). The FCU is supplied as a (junction box) spur from the ring main.

I have removed the fan heater and installed an electric towel rail. However, when I connect up the towel rail to the FCU it won't work. I have tested the towel rail by means of fitting a 13A plug and it's definitely working. The FCU supply live tests live, as does the load live when you switch the FCU on without the towel rail connected. However, once the towel rail is connected and you switch the FCU, both the supply and load lives disappear?? Have changed the FCU - same problem.

Am I doing something very wrong? Grateful for any advice - the towel rail is certainly <13A.

 

[scarypants]

have your connected it right?
radiator cables in to load side of FCU and cable supply at supply side!

 

[Steviec9]

definitely - double checked.

Supply live RED to supply live terminal
Supply neutral BLACK to supply neutral terminal
Rail live BROWN to load live terminal
Rail neutral BLUE to load neutral terminal
Earths to earths terminals

 

[VanSolo]

How are you testing the "lives"

 

[scarypants]

is the fuse ok

 

[Steviec9]

Main tester - direct test screwdriver. Again, I've tested this elsewhere and it's working OK.

Changed fuse to make sure - it must be OK because I get a live indication from the load terminal when I switch the FCU on (without connecting the towel rail)

 

[scarypants]

Don't trust neon screwdrivers, should not be used, should not be sold!

 

[Steviec9]

Fair enough. But stopping selling mains tester screwdrivers won't make my towel rail work.....

 

[scarypants]

but we can not confirm a working supply.
You said you fitted a 13amp plug to rad and worked ok.
We now need to find out if the FCU has a supply source, you need to find where it is spurred from and prove that the supply is still connected up

 

[Steviec9]

The fan heater it originally supplied worked fine, so we must assume supply is OK. All I've done is remove the heater - I haven't changed any wiring beyond the FCU, so shouldn't affect the FCU?

 

[scarypants]

If that's true, it's strange.
Have check that the breaker has not tripped on the circuit?

 

[Steviec9]

No problems at all with fuses/breakers when you switch the towel rail on, just nothing happens except for live indication immediately disappearing from both live terminals in FCU. As soon as you turn FCU off, live returns to supply terminal - no other problems occur, no tripping, blowing etc.

It defies logic. The ONLY thing I think it can be is the towel rail itself and yet, as I say, when I put a plug on this and plug it in - it works.

I'm going to test another appliance (radio or something) off this FCU later this afternoon and see what happens.... going to nip to pub for a bit of light relief first.... it's winding me up... Thanks for help so far - I'll report back.

 

[scarypants]

That sounds a good idea, how big is rad what power rating is it and what size fuse have you protecting it in the FCU

 

[VanSolo]

Reverse polarity on the line side of the FCU I reckon. The radio will work ok.

 

[Steviec9]

200W element (it's only a small towel rail), 13A fuse, per installation instructions.