On 14 Oct, 09:07, YAPH wrote:
Bits of the disintegrated old washer still stuck in the valve preventing
the new washer seating properly? Rubber washer over-tightened when system
hot and squeezing off its seat? (Usually ****es out if you do this.)
Failing that replace the DOC.


Following your lead I had a good look inside the body of the tap,
wearing my trusty camper's head torch for lighting. Near the drain
"part" that comes off at an angle from the threaded "part" I saw some
"crap" that wouldn't budge by scraping. I fitted a wood drill bit into
my electric screwdriver and set to work on the "crap" trying to avoid
the thread on the body of the tap. After about 30 seconds the "crap"
dislodged. The "crap" turned out to be a blob of solder from when the
drain tap was fitted. How the thing ever sealed in the first place I
don't know. I refitted the washer to the threaded "part", reassembled
and closed the tap, just hand tightening - and bingo, by jingo, no
leak.

Hooray! Hooray!

As a by-product, when I do drain the system (at which I am becoming
most adept), the water just gushes out of the drain when the tap is
opened. Before the drain rate was a dribble and took over an hour.
Draining of the CH system can now be doen in 10 minutes.

I had already bought a replacement drain tap for £2 but fitting it
would have involved cutting off the old one that was soldered on -
which would then have made the pipe too short - which would have
involved fitting on a new length of pipe to fit the new drain tap ....



There's a lever on the valve to open it manually - try that. Otherwise it
suggests an air-lock somewhere preventing hot water circulating around the
rads. Is there an air bleed valve on a vertical leg of pipework somewhere
you've missed, or an automatic air bleed valve that's got its dust cap
screwed down or is not automatically bleeding? (Try loosening its screwed
cap to see if that lets air out.)


On the body of the valve there is a side lever and a top lever. The
top lever seems very "loose" and the side lever resists manual
adjustment. I don't want to break them by forcing them so I haven't
manually adjusted the valves.

I can't find another air bleed on the pipework - doesn't mean there
isn't one.

There does seem to be an automatic bleed next to the boiler - it is
covered in what looks like limestone ! I guess the valve has
overflowed (from time-to-time) and this deposit built up. I have no
idea if this valve now works. I underscrewed the dust cap but nothing
seemed to happen.

Having talked to a couple of people we now thing the pump maybe
faulty. The argument goes:

I put X400 desludger in the system a couple of weeks ago which may
have dislodged some material that has become lodged in the pump
When I touch the back of the pump, where I think the mechanical
impeller is situated, it gets hot when the boiler is on
The water pipe supplying the pump from the boiler gets hot quickly
when the boiler is on - obviously
The pipes "downstream" of the valves get hot when the controller
signals the selected circuit, CH or DHW, to be working.
So that seems to indicate everything should work ....
Now, is it possible when the DHW valve is open that heat is getting to
the HW cylinder by conduction along the (really hot) metal pipes and
just a passive expansion and hence movement of the heated water which
is then cooled by the water that surrounds it in the cylinder?
Similarly, when the CH valve is open, a similar mechanism would cause
the radiator near the boiler to be hot, the next one tepid but not
cold and in the rest of the house the rads are at room temperature?

The pump can be isolated by two valves either side so will be easy to
remove (haven't tried yet, ha !) .


It's a compression fitting, with an olive (like a plain wedding ring) on
the tubular section of the 'tail' that screws into the rad. The olive can
be set at a range of positions along the tubular bit. Have you got it
right at the end, almost off the tube? It should be far enough along that
there's some of the tube sticking into the mating part of the valve body.
(Have a look at how any other compression fitting works so you know how
it's supposed to be.)


Finally the leak seems to have stopped. I'm really nervous about
disassembling it again and possibly recreating a leak - especially
based on the problems I have experienced with the drain tap leaking. I
know that is ignoring something that might flare up in the future but
let sleeping dogs lie.

Clive