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[padster999]

I've recently had underfloor heating fitted to my bathroom, but when it's switched on it trips the electricity in the house. I have had the wires tested that are under the tiles and it appears that the earth wires has crossed with the neutral wire. When I connect the heating using the live and neutral (no Earth wire connected) the system works fine and heats the tiles.
I want to know if this is safe to use like this. The tiles are sealed and grouted using a water repellent and the matt is laid into the sealant below the tiles.

[sparx]

do you mean the neutral is shorted to earth?
DO NOT USE without earth connected, for safety reasons the only way underfloor heating can be used in a bathroom is with an 'earthed metalic sheath', this installation is reportable under bldg. regs part P. so should have been done by registered electrician who would have tested circuit in order to issue you with obligatory test sheets! It's the law as diydoc keeps saying......
Sparx

[padster999]

yeah I think the earth is shorted to the neutral. The heating works fine without the earth connected. There is an earth on the other side of the thermostat and also a fused switch between the thermostat andf the fuse box, would this not protect me from any problems ?

[sparx]

NO it won't, you might think your tiles & grout will keep heating mat dry but it won't for long, as the element must have been damaged to get the N-E fault how long before Live touches earth which is totally surrounding the element.When this happens if not right near the start of the mat every part of your floor will be 'live' and without earth connected may take a long time to blow a fuse.
If you are wet and touch say an earthed metal object ie a tap whilst standing on the floor it only takes 30mAmps for a few milli-second and you are 'brown- bread' .......but it's your life, enjoy
Sparx