I recently did some work to my system (replaced two radiators, and one
TRV). I too suffer from regular topping up. I suspect this is from
small leaks at the BSP tails and/or the pipe/valve joints. If the
leaks are small enough then the water evaporates from the heat before
you notice it.

Anyway, the interesting thing I found was that the system holds approx
50 litres of water, yet it only takes loss of 1 litre to cause the
pressure gauge to drop from 1 to almost zero (on a 7 rad system with a
really old Valliant combi).

I used to get concerned when the gauge dropped this low, but not
anymore.

If you have a leaking BSP tail / rad joint then it can be re-taped
(PTFE) without draining the system. Just shut off the rad valves, and
put a towel down to catch the leakage. Use a BSP plug to cap off the
rad while you are re-doing the PTFE tape. I did this last week for
two new radiators, and only lost 0.5 litres per radiator.

Ian

Andy Hall wrote in message . ..
On Wed, 20 Aug 2003 06:02:15 GMT, (Frank W) wrote:

On Tue, 19 Aug 2003 21:51:50 +0100, Andy Hall
wrote:



It would be a good idea to find out and fix why the pressure is
dropping. If this is an ongoing occurence, you may have a leak
producing enough moisture to set up the conditions for rotting of the
timbers of the house, and that can be very expensive to fix.

Andy, It currently needs topping up about once a month whan the system
is in use. Is that excessive? I cannot find any leaks in the plumbing,
but I haven't taken the floorboards up to check hitten pipe joints.

This would be really difficult to find, especially if it's a smallish
system, because the amount of water involved is small.



There are such things, but they are relatively expensive for what they
are in order to comply with water regulations.

Any idea how expensive? Would it be possible to something up using a
one-way valve and some sort of pressure operated valve?

The reason I'm interested in this idea is because I want to rent my
house out and go away for a long period. I don't want to have to rely
on the tenants to keep the pressure adjusted... Chances are they'd
just not bother - or forget...

Thanks...

Frank

I remember seeing these illustrated on one of the large plumbing
suppliers and/or manufacturer's sites a few months ago. I'm thinking
that it was BES or RWC but can't see them on either - possibly they
have stopped them. I'll look again a bit later.

At any rate, they consisted of a small open tank rather like on an
open vented system, a pump to produce the pressure, a non return valve
and a pressure sensor switch. I seem to remember them costing in the
hundreds of pounds which seemed outrageous for what they were. I
would have thought that they were more intended for commercial systems
of much greater capacity, where for similar reasons to your situation,
you don't want people dinking with the system.

Take a look at Ed Sirett's Sealed System FAQ for some ideas because
this should be fixable.

One thing to look at is whether the non-return valve is allowing a
tiny amount of backflow. Try disconnecting the filling loop (which
you are supposed to do anyway) and see if there is any sign of
seepage.

Another thing that you could try for this level of leakage is a leak
sealer treatment which is introduced into the system via a radiator.
Reports of this approach in situations such as yours have been good.





.andy

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