On Wed, 1 May 2019 10:23:48 +0100, Steve Walker
wrote:

snip

So, this suggests to me that the valve itself is faulty (damaged ball
etc) and whilst I'm more than happy to change the entire valve body
(it's on fairly short pipes that may need some 'persuading') it looks
like the valve itself is secured to the face of the valve body with 4
screws and sealed with an 'O' ring and so, might be swappable with
another / new / good unit?

http://www.freeheatingadvice.com/wp-...valve_ball.jpg

I have seen just the bodies available new for around 20 quid so this
would just cost the elderly lady that plus fresh inhibitor etc?

Worth a go ... or what are the chances the valve seats are worn etc?

I would think it more likely that they will need cleaning up.

Just or as well as replacing the ball?

The ball
is often some sort of "rubber" and the seats can end up with a rough
ring of rubber stuck to them as the ball deteriorates.

Understood. I think the ball must have deteriorated fairly badly (on
one side possibly) because the rate at which both outlets heated with
the valve in the CH position was pretty similar?

The ball also
moves only a few millimetres and arrives at the seat flat on, so there
is little chance of seat wear.

Understood.

So, are you confirming that the idea of just swapping the valve mech
should be worth a shot?

Cheers, T i m