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 thest 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?

Fatboise wrote:


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.

I couldn't have explained it better myself. ;-)

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

If there's any leaks from valve glands, water may leak out with the
pump off. The water might evaporate from the warm metal & the leakage
rate may be tiny, so you may not notice any leaks.

With the pump on, the water pressure at some parts of the system could
become negative, i.e. 0 bar gauge pressure. Any such leaks will then
let air leak into the system. Air is less viscous than water, so the
leakage rate of the air will be greater than the rate at which water
leaks out with the pump off.

This is less likely is you're pumping away from the expansion vessel.

You can also get oxygen leaking into the system through non-barrier
plastic pipe. This usually causes a corrosion problem. It doesn't
involve the system water pressure.

Aidan, Thanks for the input I have a better understanding of what is going on now.