Underfloor heating tripping RCD

[hughjayteens]

Hi All,
I moved into a house last year which has warm-up underfloor heating fitted in the bathroom. Has always worked fine, but when a colleague had it fitted at his place, the sparky had fitted it on an RCD (for obvious reasons) so I checked mine and found it to just be on a 3A switched fused spur.

I decided to change this for an RCD to be on the safeside, so did that over the weekend. Everything was working fine, but when I woke up this morning the RCD had tripped and the floor was cold. I reset it and it came back on fine, and was on and warm when I left the house, but what could be causing it to trip?

The thought of taking up the slate floor to re-lay the heating doesn't appeal in the slightest, but I obviously need to know things are safe.

I know the official response will be to get someone in to test it, which I will do if necessary, but is there anything easy I can test myself?

Cheers

 

[breezer]

if the only thing on the rcd is the underfloor heating its a fair guss to say the underfloor heating is at fault, getting some one in will only prove it

(could alwys try a differnt RCD thogh)

 

[ericmark]

RCD's have been required on under floor heating in bathrooms for a long time and one wonders why yours did not have one? Maybe it was faulty when fitted and person who fitted it did not want to rip it up either! There are clamp on meters that will measure earth leakage and also special meters to test earth leakage trips both cost a lot of money. Also you do get faulty RCD's but they are rather expensive to change in case.
Also meters to test insulation resistance again they cost.
Since it is a bathroom you should have Part P either through LABC or by using a registered electrician so since the latter is likely to have all the meters you need it may be worth getting an electrician to look at it for you.
There are bigger RCD's available but the regulations stipulate a 30ma one.
Eric

 

[hughjayteens]

Been doing a bit more investigating, and it appears that it only trips when the heating comes on - i.e it works fine while the heating is on, and when it goes off, but as soon as the time switches it back on, it trips again.

Warmup give some resistance tests on their site so maybe I'll get the multimeter out and see how it stacks up. Could it be a faulty thermostat/timer?

Cheers

 

[Pensdown]

It sounds like the heating mat maybe damaged. Although it's only an educated guess, it could be that when it's off the damaged area gets moist which would cause the RCD to trip when it first comes on but as it warms up it maybe drying out just enough to allow the RCD to stay in.

It's not unusual for the mats to get damaged when the tile adhesive is being spread.

 

[hughjayteens]

It trips out overnight even when the bathroom hasn't been used, so I am not sure moisture is playing a part, but as you say, the mat could be damaged.

Bearing in mind I have lived here for a year with it on every day, does this mean I have been at risk!?

Regs aside, what are the implications of fitting a larger RCD?