A few CH questions

[Fatboise]

I have a sealed ch system that is losing pressure over time and hav

searched throught he foroum for similar problems and have one or tw 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 mont time frame. I noticed that the towel rail in the bathroom was no heating the top bars (this is the highest point in the system). I blee the rad and the coil in the HW cylinder which is at about the sam height and it also had a lot of air in it. There is inhibitor in th 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 two storey house)?

If pumping away from the expansion tank, the pressure at the pum 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 th 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 hol pressure for a sustained period, say 1 year

-- Fatboise

[Fatboise]

I have a sealed ch system that is losing pressure over time and hav

searched throught he foroum for similar problems and have one or tw 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 mont time frame. I noticed that the towel rail in the bathroom was no heating the top bars (this is the highest point in the system). I blee the rad and the coil in the HW cylinder which is at about the sam height and it also had a lot of air in it. There is inhibitor in th 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 two storey house)?

If pumping away from the expansion tank, the pressure at the pum 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 th 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 hol pressure for a sustained period, say 1 year

-- Fatboise

[Andrew Gabriel]

I have explained a few times why air leaks in to a pressurised sealed system. See:

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

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

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.

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.

[Aidan]

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

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.

[Fatboise]

Aidan, Thanks for the input I have a better understanding of what i

going on now

-- Fatboise