Finding a leak - cold water pressure test conflicting results

[Anton1990]

Hi, I'm new here and appreciate any help or ideas on the below.

I suspect there's a underfloor leak as I have a damp patch on the wall, rotten floorboards and skirting boards between the bathroom and the living room. Leak tracing (gas, thermo, acoustic) concluded there is no leak despite the pressure tests indicating a drop in pressure.

The pressure test is done by connecting the gauge instead of the washing machine and normally on shutting the stopcck the pressure drops from 2-2.5 bars (while no taps or toilet are leaking) to 0 in around 1 min. However lately I realised that when doing the pressure test first thing in the morning (before using any water) the pressure does not drop. After the use of taps or flushing the toiler the pressure again starts dropping rapidly.

It is a one bedroom ground floor flat with a combi boiler.

Could these changes in pressure be caused by a water leak or should I look elsewhere?

Many thanks

 

[Chuck]

Try not to jump to conclusions too soon, but the morning result suggests that there is a low probability of a leak in the cold water pipework. (Not 'zero', just 'low' because some leaks are temperature dependent.) That just leaves the hot water, central heating, drains, penetrating damp, roof leak, condensation, failed damp-proof membrane, etc. to consider.

Who did the 'leak tracing' and what exactly did they check? When they didn't find a leak, what did they advise as the next step?

What shape is the damp area on the wall? Is it an external wall or internal?

Is the central heating losing pressure?

 

[Anton1990]

Try not to jump to conclusions too soon, but the morning result suggests that there is a low probability of a leak in the cold water pipework. (Not 'zero', just 'low' because some leaks are temperature dependent.) That just leaves the hot water, central heating, drains, penetrating damp, roof leak, condensation, failed damp-proof membrane, etc. to consider.

Who did the 'leak tracing' and what exactly did they check? When they didn't find a leak, what did they advise as the next step?

What shape is the damp area on the wall? Is it an external wall or internal?

Is the central heating losing pressure?

Hello Chuck,

Thank you for your reply.

It was plygon who did themal, acoustic and gas tracing and also sampled the plaster from where the damp patch is and the result was a mixture of salts so inconclusive. They did not advise the next step but only reported to the insurance company that they couldnt find a leak. It is an internal wall and the damp patch is horizontal around 1m above the floor (picture attached).

The central heating is not losing pressure but this morning I repeated the pressure test. The pressure again was not dropping first thing in the morning, I repeated the test after running cold and hot water (after running hot the pressure actually went up but think it was as the boiler was still running). After flushing the toiler and waiting a bit, the test was run again with the pressure dropped rapidly. Repeated the test later and the pressure dropped quickly again.

I am now planning on fitting a stop valve next to the toilet and use dye to monitor. I'll update as soon as I have more details.

 

[Chuck]

Hmm. Is there another flat above you? Where is their bathroom located? Is there a shower right above the problem area by any chance?