I have a sealed ch system that is losing pressure over time and have searched throught he foroum for similar problems and have one or two question that I hope somebody out there can help me with.

I set the cold pressure to 1.1 bar and it fell to 0.5 over a two month time frame. I noticed that the towel rail in the bathroom was not heating the top bars (this is the highest point in the system). I bleed the rad and the coil in the HW cylinder which is at about the same height and it also had a lot of air in it. There is inhibitor in the system but I plan to add some more.

- How good is the Fernox central heating sealer?
- Where should the automatic vent be (mine is on the bottom floor of a two storey house)?

If pumping away from the expansion tank, the pressure at the pump inlet
will be SP, pressure at pump outlet will be SP+PD.

If pumping towards the expansion tank pressure at pump outlet will be
SP. Pressure at pump inlet will be SP-PD. NB this could be negative at
the pump inlet and for some way upstream, especially at high level. Air
will leak into the system.

- Can sombody explain to me how the system can get air into it if the pump is pumping towards the expansion vessel ?
- How does one test if the gas in the system is hydrogen?
- Is there such a thing as a totally sealed system that will hold pressure for a sustained period, say 1 year?

In message , Fatboise
writes

I have a sealed ch system that is losing pressure over time and have
searched throught he foroum for similar problems and have one or two
question that I hope somebody out there can help me with.

Two boilers with the same problem ?

Drivel will be along shortly


--
geoff

In article ,
Fatboise writes:

- Can sombody explain to me how the system can get air into it if the
pump is pumping towards the expansion vessel ?

I have explained a few times why air leaks in to a pressurised
sealed system. See:
http://groups.google.com/group/uk.d-...e52b674cf9ad5c

- How does one test if the gas in the system is hydrogen?

With a lighted match -- hydrogen burns with a dim blue flame.

- Is there such a thing as a totally sealed system

No. There will be microscopic leaks at every valve stem and
anywhere else where a moving part passes from the outside
into the water flow.

that will hold
pressure for a sustained period, say 1 year?

I achieved better than that on an all-new heating system,
where I pressure tested each section during construction.
IIRC, there was no drop at all for first 18-24 months.
However, after a few years, things start to deteriorate.
So far, the weakest link in my system seems to have been
the O-rings used on the radiator blanking plugs, for which
I've had two which started leaking, resulting in a loss of
pressure of something like 0.1 bar/month, but more noticably,
you start hearing air in the system (tiny bubbles).

On neither occasion were my leaks enough to see any water
leak out, as that rate of leak dries up before you notice
any moisture. One way you might actually see leaks it to
wait until the heating is off for the summer, and then
top-up the system to increase the pressure to the normal
max operating pressure you would see when the system is
hot. Leave it for a day, and then go around checking every
valve, radiator, joint, etc for leaks, as with the system
cold, the moisture might now stay around long enough for
you to feel it. I suspect you will never get any older
system sealed well enough to last a couple of years with
no pressure drop -- you are never going to have all the
components in good enough condition.

--
Andrew Gabriel