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Discussion Starter #1
One for the electrical experts on here...

About 2 years ago, as part of a kitchen renovation, we had electric underfloor heating put in to the enlarged kitchen space. The feed for it is direct from the consumer unit, in which there is a dedicated 16A circuit breaker. The feed runs to a switch, and from there up to the thermostat and control unit. Originally the switch was a fused spur with a 13A fuse.

After about 6 months, the switch failed in that it would connect intermittently and you couldn't physically turn it off, it seemed to be mechanically broken. I assumed it was just faulty and replaced it with a new one, although a plain white plastic one this time. That lasted a few weeks until it was broken by the dog bed whacking it, so replaced again, with a low profile metal one.

About a year later, it started doing it again - noticed that the controller was clicking on and off, and found that the switch was again mechanically buggered. Thought then was that a standard fused switch spur was not up to it, so this time it was replaced with a 20A rated switch.

Less than a month later, the new switch is now doing exactly the same, if it's on, the controller just clicks on and off constantly, and the switch itself, whilst it will turn off, won't stay off. Rather than clicking into the off position, it just returns to the on position, very similar to the other switches.

So what's going on? The switch is always on, we never operate it, so there's no reconnecting that might cause internal sparking, etc. It's rated at 20A, which it shouldn't ever get near as the circuit breaker would have popped before that point (it never has, and neither did the old 13A fuses). I am assuming that the current flow through the switch is somehow heating it up and damaging it, but how could it be?

What then to do - just buy another 20A switch and hope for the best?
 

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I’ve been sparkying for 30+ Years, and that is an odd one, I agree it’s probably the load on the contacts to the switch, but usually it’s when they get turned on and off a lot.
Other reason it could be is that the accessory might be a bit shit.
It should really be on a fused spur, fused to the rating of the mat, which should be on the box, I’ve seen Spurs melt quite often, with higher load applications it’s better to get a decent spur, like an MK or Crabtree, the ones from screwfix are generally made from cheese.

And when you connect it, make sure the terminals are tight!
 

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Discussion Starter #3
I've been sparkying for 30+ Years, and that is an odd one, I agree it's probably the load on the contacts to the switch, but usually it's when they get turned on and off a lot.
Other reason it could be is that the accessory might be a bit shit.
It should really be on a fused spur, fused to the rating of the mat, which should be on the box, I've seen Spurs melt quite often, with higher load applications it's better to get a decent spur, like an MK or Crabtree, the ones from screwfix are generally made from cheese.

And when you connect it, make sure the terminals are tight!
Thanks for the input, I have ordered a new MK switch to pick up and fit later, and will make sure that the terminals are well connected. It's all Prowarm stuff that has been fitted, all specced and installed by the same electrician, who also did the new consumer unit and the new cable to the UFH itself, so I am hoping that it's all good apart from the switch. The whole house electrics were checked and certified at the start of this year, so I wouldn't expect any issues.

It just needs to work for another month and we should then be moved (although the new place also has electric UFH heating in places).
 

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Discussion Starter #6
Now swapped out for a new MK switch and up and running again. The old generic switch had clearly got hot around the live supply terminal and melted the plastic a bit, knocking the switch internals out of alignment enough to cause the symptoms described.

I *think* it was because I hadn't tightened the terminal properly last time, and perhaps there was some resistance as a result (and therefore a heating effect). I'll keep an eye on this one, but have made sure I tightened them properly.
 

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Now swapped out for a new MK switch and up and running again. The old generic switch had clearly got hot around the live supply terminal and melted the plastic a bit, knocking the switch internals out of alignment enough to cause the symptoms described.

I *think* it was because I hadn't tightened the terminal properly last time, and perhaps there was some resistance as a result (and therefore a heating effect). I'll keep an eye on this one, but have made sure I tightened them properly.
Loose terminal screws cause a whole load of problems, it causes a load of heat through resistance if they are loose, and it only gets worse.
Shower switches go all the time, and they melt back the cable by as couple of inches.
You have to make sure the cable hasn't discoloured from the heat, it needs to be shiny copper or it will just do it again.
 

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Discussion Starter #10
Loose terminal screws cause a whole load of problems, it causes a load of heat through resistance if they are loose, and it only gets worse.
Shower switches go all the time, and they melt back the cable by as couple of inches.
You have to make sure the cable hasn't discoloured from the heat, it needs to be shiny copper or it will just do it again.
It was discoloured, so I chopped that bit off and it's now shiny copper well tightened down. The one I took off was Crabtree, now it's MK, and the MK one has the terminals more separate from the switch, so hopefully it will be OK now.
 
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