How do I find a mysterious leak from a cistern/pan?

[trwb99]

Hi All,

I have just had a new toliet and cistern fitted and we have a very slow leak - slow enough to stain the floor over one square metre during 72 hours. The problem is that I can't find the leak.

It only happens when the water flow to the cistern is on, not when the cistern is full, the pan is full but the water is off - suggesting it starts from the input pipe, where this enters the cistern - but as the leak is so slow, I can't identify the source.

Anyone have any ideas on how to be sure of the source of a leak - is there a spray for example which will change colour on contact with water? Or any other ideas? I have had my head behind the toilet for a week now and am running out of patience!

Cheers

Tom

 

[kevplumb]

chalk dust or talc

 

[Igorian]

I have had my head behind the toilet for a week now and am running out of patience!

Must be quite difficult to type from there

 

[Bahco]

Try placing coloured tissue strategically at all the points where it is possible to leak from.
Could be you have a hairline crack under your pan.

Meanwhile, you can come out of the toilet now.

 

[brumylad]

It might just be leaking while being flushed

 

[bathjobby]

You sure it isn't condensation when cold water first enters cistern ?

 

[Panjandrum]

It only happens when the water flow to the cistern is on, not when the cistern is full, the pan is full but the water is off

How do you know this?
I've had similar symptoms from condensation or from connection to bottom of cistern not being quite tight enough.

 

[--tom]

Seen on an American plbg. forum:
isolate the water supply to that WC
flush the cistern
wipe and dry the cistern exterior
fill the cistern with warm water, eg. using a pan, the warm water being less likely to create condensation.
flush cistern
repeat process
this will indicate wether it's condensation or a leak - hopefully.
it was also claimed that putting a little food dye into the cistern will give an indication of whats happening

 

[brumylad]

thats a clever idea.........warm water.....I like that.

 

[--tom]

Also from USA site: Watts 4a818 tempering valve.
It pre-mixes the hot and cold water before supplying the WC so that you have warm water entering the cistern.
Quite simple to fit but what the UK regs say about such a device i dont know.