All,

Basically, the downstairs radiators aren't working.

Central heating system: newly installed (three months ago) boiler
(downstairs) and hot water cylinder (upstairs). System upgaded from
pumped HW/gravity CH to fully pumped system. Pump in airing cupboard
beside HW cylinder, one of those three way motorised valve thingies
also in airing cupboard (which works).

Last week, before we switched the central heating on, I removed a rad
in upstairs toilet to knock down wall (see other thread "Bathroom from
scratch"). While removing the rad, I mde on of the valves leak, so
had to drain the system and put an end stop on one of the pipes to the
rad.

This was the first time I had drained a system, and I refilled it by
untying the ball cock to header tank, then bleeding all the rads. As
it was an emergency, 10pm at night, I did this without consulting the
archives on here and bled bled the upstairs rads first, then
downstairs, susbsequently finding out that this is the wrong way
round. I haven't yet redained the system and refilled corectly.

On finding that downstairs rads weren't working, I did a few searches
on here and tried the following:

- bled pump and checked that the impeller isn't stuck. No air came
out of pump, and impeller spinning freely.

- switched off all radiators apart from one downstairs furthest away
from pump/HWC, switched on heating...the rad which was previously
stone cold warmed up within 1 minute...very hot to touch. Bingo I
thought. Switched the rad off and did the same to all downstairs
rads...switching of all rads apart from the one I'm working on...each
heated up nicely. I also bled each one as it was switched on and hot
water came out.

- when I switched on all the rads..again, only the upstairs ones warm
up. This morning, every downstais one was stone cold, whereas before
they were all slightly warm to touch, but not hot like the upstairs
rads. The one in the downstairs bathroom is still stone cold.

I'm not sure what the problem is...each rad will heat up very hot if
it's the only rad on...but switch them all on and the downstairs ones
don't warm up. I'm pretty sure the pump is OK as a solitary switched
on rad, no matter where in the house will heat up almost
instantaneously.

Is this an airlock? It's just that I'm reluctant to call out the
plumber/heating engineer that installed it as he's a really nice chap,
and I don't want to look like a mug. Also, the rad ai removed will be
going back on, after the weekend,and I don't want to have to call him
out when I drain the system again and refit the rad. If I can't get
it to I'll call him out after I've refitted the rad...but would like
to at least have a warm shower room before...and it's not really in
the spirit of uk.diy....

Another question...when bleeding the pump via the big brass screw on
the back while the pump is on, is it normal to only have a little
dribble coming out...I would have thought that it would spurt
out...but would be happy to be wrong...

Many thanks for your help chaps...

Mark