Remind me of the original problem - it seems a long time since I wrote the
above!


Aye, just about a month ago now

A description of the system - including the relative position of boiler,
pump, zone valves, etc. would help. Even better if you can take some photos
and upload them to a website and post a reference to them.

Here's the description I posted first time, aswell some other bits I posted:


Quote
My system consists of a Baxi Bermuda located behind my gas fire
downstairs. The pump is under the downstairs floorboards. I think (but
I'm not sure, sorry) that the HW is circulated by gravity. I really
couldn't answer about the motorised valve. I haven't noticed any around
the pump or in the airing cupboard, but this doesn't mean there aren't
any (it's generally inconvenient getting to the pump)
Unquote

Quote
Anyway, My central heating pipes/rads make quite a lot of noise of
running water, particular upstairs and in the pipes going to upstairs.
The radiators upstairs are a nightmare. One of them is relatively ok,
heat-wise, but it needs bleeding every 2 or 3 days. The other radiators
are cold and appear to be empty. If I open the bleed valves on these
with the thermostat set so the pump and heating is running, then water
drains from the radiator (I can feel suction on the bleed valve.) If I
turn the thermostat so the heating is off, the radiators fill up, but
when they are full, they are still cold (getting full with cold water??)
Sometimes, through bleeding all rads at the same time and then switcing
the bleed valves off, I hear running water, then the header tank
overflow pipe starts spilling water. And that's about it, I'm not sure
where to begin to look.
Unquote

Your original reply read:

Quote
I would guess from your further information that you have no corrosion
inhibitor in your system - with the result that a lot of sludge has built
up, partially (or even completely!) blocking some of the radiators. I would
also guess that what you are bleeding out is hydrogen caused by the
corrosion rather than air. [You can test for this by holding a lighted taper
in the stream of gas coming out of the bleed valve. If it burns, it's
hydrogen!]

Sludged-up radiators would probably explain what happens when you try to
bleed with the pump running. The pump is probably installed in the boiler
return - so that it's in effect sucking the water through the radiators. If
the inlet of a radiator is blocked, and you suck on the outlet with the
bleed valve open, you're going to suck the water out. This will end up in
the header tank, with a resulting rise in level.

It seems to me that your system needs a really good flush out, and then
needs to have inhibitor added. By far the best way to flush it out -
particularly with summer coming on - is to remove the rads and take them
outside and give then a good flush out with a hosepipe. While they're off,
flush the flow and return pipes by keeping the header tank full and opening
each radiator valve in turn (with a bowl under it to catch the water!).
Incidentally, take great care not to spill any black sludge from the
radiators on your carpets - it makes a pretty indellible dye!
Unquote

Sorry to make the post so long, I just thought as most of the info was
there, I'd just cut and paste.

I'm not sure what to take pictures of to be honest, as I said, the
boiler is behind the fire, and the pump is under the floor. That only
leaves the airing cupboard & header tank...

Thanks again for your assistance,
Bob