Sppoky drain taps ...

[Jethro_uk]

Following a pre-season bleed and test run, I've noticed my combi boiler pressure dropping slowly.

I was preparing myself for an empty expansion vessel (which I repressurised a few years ago).

Then by luck, I was standing in our utility hall - less often used - and the light managed to catch a slightly darker patch on the carpet. Which was right by the square drain tap for the system.

Yup - it took 1/2 a turn !

The thing is, as SWMBO clearly remembers - that was checked 3 times last year after I flushed and re-inhibited the system. She remembers because she asked me and saw me put the spanner to it, commenting it was no harm to check and re-check.

So, not believing in ghosts, and knowing no one else has been anywhere near it, are we both mistaken in our recollection ?

Or can these things work themselves loose with heat-cycling ? Possibly more likely when old ?

I have heard of debris being trapped in the thread which crumbles, leaving it loose ?

[James Stewart]

I had that a few weeks ago pressure started falling alarmingly the leak was at a radiator hidden behind a bed...amazing the fall in pressure for such a small leak .....

[newshound]

Degradation of the washer (especially if it is rubber rather than fibre).

Oddly enough I'm losing pressure too, havn't quite got around to checking the expansion vessel, but no obvious "overflow" so I suspect I've got a similar leak.

[Brian Gaff]

Yes there is one such down in a building we frequent, it has been tightened many times. There is also another that persistently hammers though there seems no reason for it. Brian

[Roger Hayter]

IME the washers invariably harden and ultimately disintegrate when used in CH systems. This could cause the symptoms you describe. There seems to be a bizarre gap in the market for suitable washers made of heat resistant rubber. I can find no source, and have simply removed most the drain valves that the original CH installer used.