On Mon, 25 Oct 2004 16:14:30 +0000 (UTC), "Charles Middleton"
wrote:


"Andy Hall" wrote in message
.. .

Hi Andy, thanks for the reply. My comments are below ...

- If you put your hand on the pipe work in the airing cupboard (when not)
hot, around every second you can feel something almost like someone is
tapping on the pipe - a slight movement. Perhaps "knocking" would be a
good
description.

With the pump running? Otherwise pipes in another part of the system
which are getting hot or cool and are expanding or contracting.

This is with the pump running.

It could be that the pump bearing is knackered, but I wouldn't shell
out for a new pump just yet.



The system is (I'll describe as not sure on the exact description),
Gloworm
Ultimate boiler, a [something] Gold pump, has hot water tank and a small
header tank in the loft. Is this an "open vented" system? The hot water
tank
has a small tank on the top which I believe provides the head for the
system.

Could you elucidate a bit more.

Do you mean that there is a small tank in the roof and then separately
and somewhere else there is a HW cylinder with its own small tank
separate to the first?

That is what I meant. There is a small tank in the roof and the HW cylinder
has a small tank on the top of it.

That's good. In that case it's a conventional open vent system and
you can do things to the primary (heating) water without impact on the
domestic hot water.





Thinking about it, is it fare to say that the only mechanical part of the
system is the pump so It might be worth replacing this?

It could be, but there may be other issues. Can you comment on the
system first. Also important if you have a small separate tank in the
roof is whether there is enough water in it. Also the relative
positions of the vent pipe leading to and over this tank and the
feed/expansion pipe going from the bottom. It's quite important to
know where these join the main system, how far apart etc.

Hopefully comments above have clarified the type of system. I'll have to get
into the loft and have a look at hte latter points. I'm away all this week
so will need to have a look at teh weekend. To clarify ...

- The feed/expansion pipe: I presume this is what will "top up" the system
and also keep it pressurised?

Yes, but it's not a pressurised system in the sense that you might
have read about pressurised systems. They are completely closed in.
The only static pressure that you have is by virtue of the height of
the small tank in the roof.




- The vent pipe - what is this used for?

To let air out of the system and in the event of a boiler malfunction
such that it boils, steam. Some people mistakenly call it the
expansion pipe - it isn't.

The pipe near the bottom is called the feed/expansion pipe because it
allows the system to be filled and as the water is heated, it can
expand back up into the tank.

In a correctly designed system, these two pipes should join the main
circuit within about 150mm of one another and definitely not on
opposing sides of the pump. Sometimes they join at a little chamber
called an air separator which is used to make convenient connections
and get air out of the system.

If the connections are not to the right places, or are too far apart,
then there is a pressure differential and either air is sucked down
the vent pipe or water pumped over. You may have the first of these,
but it's not so obvious to see as the pump over case. Often it
happens when motorised valves are changing or when the the pump
starts.

Another possibility is that there is too little water in the small
tank and when cold some air enters the system down the feed pipe.
Often this is because the ball valve is stuck and the cure is simple.
When the water is cold you need say 50mm depth above the feed pipe at
the bottom - no more because you need to allow for a rise in the water
level with expansion.

It's possible that corrosion is happening in the system. That would
be if there is no inhibitor and if the escaping "air" from when you
vent is actually hydrogen and burns with a small blue flame.

The source of the gas/air in the system does need to be investigated
and fixed. If you are into doing some plumbing, information on how
to fix the vent arrangement if this is what it seems to be can be
provided here - helpful if you can put some photos on a web site.

I wouldn't spend money on a new pump at this point, but it could be
worth turning it down a notch as suggested and see if the venting and
noise issues reduce. If they do, then you have your culprit.


..andy

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