I kept getting a whiff of damp plasterboard every time I went in one of our
bedrooms which is unused, but I couldn't figure where it was coming from.
The walls are plastered blockwork, not board. Then, Friday, I happened to
stick my head in the airing cupboard, and got another whiff. Looking up, the
ceiling was clearly damp. The loft hatch is just in front of the airing
cupboard, and I knew that the main and central heating header tanks were
just above there, so I went up to take a look. The ball valve for the main
water tank was leaking - from the threads ...

I shut the water off and unscrewed the union to get a look at the fibre
washer, which as it turned out, was not in particularly good condition. Nice
easy one, quickly fixed, I thought. However, even after cleaning the seat
down and the mating face on the (plastic) ball valve thread, and fitting a
new washer, there was still considerable seepage from the threads end of
things. I unscrewed the union again and had a close look at the threads, and
several were quite badly damaged around the top. It was too late by then to
go and get any parts, so I just wrapped a bunch of PTFE tape around it, and
screwed back up. I left a bowl and towel under it overnight.

Saturday, I had a close look at the whole thing, and decided that the ball
valve was well clagged up with limescale, and wasn't sealing very well
either, so I would just start again with a new one, and fit a service valve
to the split feed for the two tanks whilst I was at it. Once the old valve
was off, I was able to look at it a bit closer, and there is definite damage
to about three thread turns for about a quarter the way round each turn.
Bear in mind that this is the original ball valve, 20 odd years old, and had
never leaked up to this point. So what has caused this ? About the only
thing that I could come up with was that the tank is plastic, and the high
flow pumped shower that I run probably beats the water inlet, so allows the
tank to empty a fair way - certainly you can hear the tank filling for a few
minutes after a shower has been finished. This would cause the sides of the
tank to flex, and the ball valve with them. The feed pipe was rigid copper,
so a considerable strain would be put on the coupling as the tank flexed,
and also as the tank reached full, and the float force was exerted on the
valve. I reckon that this has caused the damage to the plastic threads and
the fibre washer, and initiated the leak - or am I barking up the wrong tree
altogether ? This time, I have fitted a metal high pressure ball valve, and
'decoupled' any movement from the rigid feed pipe, by putting a flexi in the
line. Does that seem like a good move ? All the plumbing is at least dry
now, but I think that the wood tank platform is going to take some time to
dry out, unless I hurry it along with a fan heater up there for a couple of
hours ...

Arfa