Help finding a leak

[Trish0608]

Hello,
I need help trying to figure out how water will travel through a plaster board ceiling so I know which pipes to check or if all floor and landing has to come up. Is it likely to go with the joists or can it go under them? What ever it is its a slow leak and I can't see any evidence of where the water is coming from.
There is a damp area in the middle of my hall ceiling, its been there a while I thought it was a stain until I covered it with smoothover and it bubbled so I scraped it and all plaster and prob years of paint came off back to the bare plaster. I used a moisture tester on it and its over 50%.
It is directly below the doorframe to the bathroom. I managed to get part of a board up. There are no pipes above it, they run around outside edge of room. The joists run left to right when you stand in the doorway. The sink is directly in front of you and the hot water tank is on your right, both have pipes level with the patch but 2-3ft away. Any ideas? Thanks

 

[Phill Peck]

i would guess at a pinhole in the bottom of your hot water cylinder.

water will normally not pass under joists but run between them and come out on a join between the plasterboard

if there are no pipes there you should be able to see staining on the joists which should give you an indication of direction

 

[bengasman]

Water runs in a totally unpredictable way, you may be lucky but be prepared to pull the floor up.

 

[Trish0608]

Thanks for replies.
I just looked under the floor by the hot water tank and there is a line of bricks under the floor - must be top of downstairs wall???blocking the way the water would come so now I'm wandering about the chance of water coming that way without finding somewhere else to pool first. The pipes are sitting in a notch on top of joist though. Some one in work suggested a hairline crack in my cast iron bath so I will look under it again next time its full but looked bone dry under there other day.

 

[DeltaT2]

We bought a USB Endoscope on eBay for about £20, it's great for this kind of thing, but you need to get the area well lit with a torch or light. Link it to your Laptop - great bit of kit!!
Hope that's of some help?

With 38 years in the trade, I'd advise looking at the shower(if you have one?) first, every time.

 

[Trish0608]

I have looked under the bath, its old cast iron one from 70's and its held up by 3 metal legs and some bricks in one corner where the leg fell off at some point (its under there too) Is there a chance this has damaged the bath to give it a slight leak, or if the bath was cracked would I REALLY know about it.
Sorry if these sound like daft questions but I am totally new to DIY that doesn't involve slapping a bit of paint on and I'm trying to learn.
Thanks

 

[DeltaT2]

If the bath was leaking, you'd clearly see staining on the floor or indeed a wet floor. If you don't have a shower, then it sounds like an underfloor pipe. Why not post up some photos hen - that always helps.

 

[Happyplumber]

good to see your back Dickie and behaving yourself,may it last