When I refill the system the lowest radiator fills quite quickly but then
nothing seems to be happening for ages. I vent the pump and go round each
radiator in turn and open the bleed valve but very little air comes out
until many hours later. Should I leave them all open and just keep checking
for the first signs of water? I also open a bleed valve off the pipe to the
hot water tank but don't leave it open.



As a last resort I switch on the pump for a while till it starts to get
warm, this does seem to speed the process up but I realize I shouldn't need
to do this.



I suppose there is an airlock somewhere in the system, probably in the
boiler, so would it be safe to connect a hose between a mains pressure tap
and the drain cock and blast mains pressure water in reverse through the
system until it appears in the header tank?



Thanks

Roger

On Sun, 11 Apr 2004 11:52:03 +0100, "Roger"
wrote:

When I refill the system the lowest radiator fills quite quickly but then
nothing seems to be happening for ages. I vent the pump and go round each
radiator in turn and open the bleed valve but very little air comes out
until many hours later. Should I leave them all open and just keep checking
for the first signs of water? I also open a bleed valve off the pipe to the
hot water tank but don't leave it open.


I wouldn't leave the bleed valves open unattended. All it takes is
for an airlock to suddenly clear and then you will be in trouble in
the worst Sorcerer's Apprentice fashion.

When the system is full, does it work properly? Do all radiators warm
up and are they poor at warming up and with cold spots around the
bottom centre?

I am thinking of possible sludging here......



As a last resort I switch on the pump for a while till it starts to get
warm, this does seem to speed the process up but I realize I shouldn't need
to do this.

This is a bad idea, because if a pump runs dry, you can knacker the
bearings quite quickly.




I suppose there is an airlock somewhere in the system, probably in the
boiler, so would it be safe to connect a hose between a mains pressure tap
and the drain cock and blast mains pressure water in reverse through the
system until it appears in the header tank?


Since you have the system drained down, I would suggest a check for
sludging. Pick a convenient radiator and place collecting vessels
underneath the valve unions. I use cat litter trays from the
supermarket for this. Take care because heating water and sludge is
an indellible dye.

If there are signs of sludging, you can try a method of cleaning whcih
I've used and described before a few times which involves taking each
radiator outside and flushing with a hose or a pressure washer.
While each radiator is removed you can flush with some fresh water
through the pipework as well. It could be that you have a build up
of crud in the pipes.

Be a bit careful if you attach a hose and blast water backwards
because you could overflow the header tank.

If there is a sludging problem, after you have cleaned the worst out
as described, you can use a chemical flusher and deal with the rest,
before flushing once more and filling with inhibitor.


If there is no appreciable sludging, then I would try to find out why
the airlocks are happening if that is what was happening. Obvious
things are poor pipe runs. An open vented system should fill OK.
Before converting mine to sealed operation, I would tend to fill the
ground floor radiators first and then the first floor. Actually I
still do.


Another option, if the boiler is relatively recent and will accept it,
is to convert the system to sealed operation. This is remarkably easy
to do and will resolve airlock problems completely. The system must
be clean of course. If you search for a post by Ed Sirett, he has
written a FAQ on how to do this.










Thanks

Roger










..andy

To email, substitute .nospam with .gl

"Roger" wrote in message ...
When I refill the system the lowest radiator fills quite quickly but then
nothing seems to be happening for ages. I vent the pump and go round each
radiator in turn and open the bleed valve but very little air comes out
until many hours later. Should I leave them all open and just keep checking
for the first signs of water? I also open a bleed valve off the pipe to the
hot water tank but don't leave it open.



As a last resort I switch on the pump for a while till it starts to get
warm, this does seem to speed the process up but I realize I shouldn't need
to do this.



I suppose there is an airlock somewhere in the system, probably in the
boiler, so would it be safe to connect a hose between a mains pressure tap
and the drain cock and blast mains pressure water in reverse through the
system until it appears in the header tank?



Thanks

Roger


How old is your system? Have you ever taken a radiator off for
decorating and did black slugde drip out of it? I had an old system,
drained it then removed each rad in turn and flushed them through with
hose pipe, some OK but some really full of sludge. Re-filled and added
flushing agent,left for a few days then drained and re-filled adding
inhibitor. Much improved for a couple of years but have have new combi
system since.

I suppose there is an airlock somewhere in the system, probably in the
boiler, so would it be safe to connect a hose between a mains pressure tap
and the drain cock and blast mains pressure water in reverse through the
system until it appears in the header tank?

Yes, do this. One of the reasons I prefer sealed pressurised operation is
that the standard filling loop does just this, making refilling a doddle.
Check the security of the overflow first, though!

If you find where the airlock is likely to be, insert a bleed valve there.
Look for large inverted U-bends.

Christian.

In article ,
Roger wrote:
I suppose there is an airlock somewhere in the system, probably in the
boiler, so would it be safe to connect a hose between a mains pressure
tap and the drain cock and blast mains pressure water in reverse through
the system until it appears in the header tank?

Yup.

--
*If you ate pasta and anti-pasta, would you still be hungry?

Dave Plowman London SW 12
RIP Acorn