Large bathroom mirror mysteriously cracked - heat pad?

[fathertobe]

We've got a large bathroom mirror 2.5m wide by 0.8m high, 6mm thick.

It's secured to the wall using these:
http://www.vola.com/Gb/Products/Accessories/T20

And on part of the back there is a heat pad:
http://www.screwfix.com/p/heated-bathroom-mirror-panel-410-x-580mm/77859

It's been up in our bathroom for over 2 years. I noticed some discolouration at the edge at the rear - black spotting - which I think is probably some water damage. It is safety-backed but when we bought it, I wasn't aware foil-backing was recommended for bathrooms.

If you've got this far, thanks. here's the exciting(!) bit:

It's cracked - a vertical line upward in around the area of the heatpad.

Any thoughts on why this might happen? Although it didn't happen in my presence, apparently no one had been pressing hard on it or anything. The pad may have been recently on (comes on with light) but not for any extreme amount of time.

Am about to bite the bullet - with foil backed this time - but it would be careless to make an obvious mistake twice ...

 

[foxhole]

Heat pad may be faulty and overheated, remove mirror and check wall, may have been slight building movement which would also crack the mirror.

 

[fathertobe]

Thanks. WIll do this and report back.

Does anyone know if heatpads can be attached to foil-backed mirrors?

 

[JohnD]

apparently no one had been pressing hard on it or anything.

'mmmmm

 

[fathertobe]

Well that's what I thought. But the person near the room at the time is an adult and has no reason not to tell the truth!

 

[JohnD]

any cracks in the wall?

I have a larger mirror where I slipped polystyrene tiles behind it so it has flat support against the wall.

 

[fathertobe]

I'll need to get it off to look... Two or even three-man job!