I have a conventional open vent CH/HW system, seperate pumps for CH and
HW with their own 2-port motor valves. Since I installed a Megaflow HW
cylinder a few years ago, it's been really difficult to refill after
draining.

Today, although the CH is working OK, the HW isn't, and the pump seized
as it got that hot and was noisy (a surfing sound). I *think* the
problem is that the primary coil in the Megaflow is air locked at the
top, and I *think* you can get various venting devices that I can fit
to the Megaflow's primary return (the higher of the two pipes - Heatre
Sadias recommendation suprisingly).

But I don't know what's available or what to ask for. And any 'tricks'
I can do meantime please?

Can anyone help please?

Thanks,

Paul.

On Fri, 18 Mar 2005 13:54:05 -0800, Paul wrote:

I have a conventional open vent CH/HW system, seperate pumps for CH and
HW with their own 2-port motor valves. Since I installed a Megaflow HW
cylinder a few years ago, it's been really difficult to refill after
draining.

Today, although the CH is working OK, the HW isn't, and the pump seized
as it got that hot and was noisy (a surfing sound). I *think* the
problem is that the primary coil in the Megaflow is air locked at the
top, and I *think* you can get various venting devices that I can fit
to the Megaflow's primary return (the higher of the two pipes - Heatre
Sadias recommendation suprisingly).

But I don't know what's available or what to ask for. And any 'tricks'
I can do meantime please?

Can anyone help please?

Thanks,

Paul.

I'm not fully convince the problem is an air lock. However assuming it is
then you have two choices manual and automatic. In particular I would
check both the zone valve and the pump first.

For a manual vent you would add a Tee into the pipe a length (say 300mm)
of pipe going vertically and finish with a manual vent like (screwfix
19155). You can use the 22mm version if that helps, or reduce to 15mm and
then the 15mm version.

For an auto vent you would ask at a shop for an 'auto air vent'. These
invariably have 1/4" or 3/8" BSP connectors on their inlet. So you will
need a 3/8-1/2 bush and maybe a 1/4"-3/8" bush. The other fitting you need
is 1/2" to 15mm (such as screwfix 12341).


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

Ed Sirett wrote:

I'm not fully convince the problem is an air lock. However assuming
it is
then you have two choices manual and automatic. In particular I would
check both the zone valve and the pump first.

Thanks Ed. In fact, I fitted an auto vent this morning. I assumed the
pump was OK, 'cos I could see the impeller spinning, and I had set the
motor valve manually open. Of course, they could still have been
faulty, but as they were both working fine immediately before I drained
the system, it would have been a bit of a coincidence if they'd have
stopped in the meantime.

Anyway, I fitted the vent with about 300mm of vertical pipe, refilled,
and expected to hear a massive amount of air coming out of the vent.
Well, it did for a moment, and then nothing. I couldn't believe it, so
I loosened the vent and water p***ed out, so it was functioing
properly.

Anyway, eventually, I got the HW to circulate (I dunno how), and it's
working fine now, but I still don't know what the problem is, so I'll
have it again next time :-(.

I might put two or three vents in strategic spots. I think part of the
problem is that the header feeds the HW primary flow (which,
unconventionally is lower than the return), and somehow things are
getting locked up as that water tries to get down into boiler.

BTW, the auto vent took a 15mm pipe, so that was easy.

Any further suggestions appreciated.

Thanks.

Paul.

On Sat, 19 Mar 2005 06:13:10 -0800, Paul wrote:



I might put two or three vents in strategic spots. I think part of the
problem is that the header feeds the HW primary flow (which,
unconventionally is lower than the return), and somehow things are
getting locked up as that water tries to get down into boiler.

BTW, the auto vent took a 15mm pipe, so that was easy.

Any further suggestions appreciated.



I take it that there is only one pipe between the header cistern and the
primary circuit? In which case the main cuase of the air-lock is in the
combined feed and expansion tank, this causes the primary circuit to be
empty with all the problems that ensue.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

Ed Sirett wrote:
I take it that there is only one pipe between the header cistern and
the
primary circuit?

Indeed.

In which case the main cuase of the air-lock is in the
combined feed and expansion tank, this causes the primary circuit to
be
empty with all the problems that ensue.

But if the cistern feeds into the flow, and the air vent I fitted is on
the return, I don't see where or how the lock is occurring. But it is!


Regards,

Paul.

On Sat, 19 Mar 2005 23:39:33 -0800, Paul wrote:


Ed Sirett wrote:
I take it that there is only one pipe between the header cistern and
the
primary circuit?

Indeed.

In which case the main cuase of the air-lock is in the
combined feed and expansion tank, this causes the primary circuit to
be
empty with all the problems that ensue.

But if the cistern feeds into the flow, and the air vent I fitted is on
the return, I don't see where or how the lock is occurring. But it is!

With only one feed/expansion pipe there is a tendency for an air lock to
form in the feed/expansion pipe. How likely this is depends on the layout
of that pipe. Once the heating circuit warms up there is a good chance
that an air lock will get pushed back into the tank and escape.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html