On Jan 18, 8:59*pm, AmateurRob
wrote:
Hello,
This is my first post - and I'm looking for some help on a Central
Heating System that's sending me mad!

I've got the following system:
- Sealed CH system in 3 storey house + Cellar (i.e. 4 floors)
- Expansion vessel in Cellar with Pressure Gauge
- Boiler on Ground Floor
- 20 radiators across all floors

Problem is I get air in the (top) 2nd floor radiator and hence a cold
radiator eventually. *I'm having to bleed it about every 2 days to keep
it from going cold. *I understand this is air getting into the system
somewhere, so I've increased the pressure to 2.0bar to try to identify
leaks. *I've found a few dodgy radiator tails and so sorted those out.
There's no sign of water in the air side of the expansion vessel. *Since
I have the pressure gauge in the cellar and then 3 floors above that,
then I also believe I need a higher intial cold pressure - so I've ended
up with about 1.8bar. *When warm the pressure only increases to about
1.9bar, so I've assumed the pressure vessel is doing its job. *I've
thought about adding some leak sealer but was trying to avoid that by
fixing the leaks 'properly'.

I can't see how the air is getting in if the system is pressurised (i.e.
if I put a needle in a water balloon to make a leak then surely only
water would come out - and no air would get in).

So I'm out of ideas and wondered if anyone could help before I got a
plumber in.

I've read the (excellent) Sealed CH FAQs athttp://tinyurl.com/4xxj27s
but still none the wiser.

Thanks in advance,
Rob.

--
AmateurRob

For air to get in, water must be getting out.
First check that no water is escaping from the safety valve. (Tape a
plastic bag over the outlet & leave for a while.)
If there is, the problem usually lies with the expansion vessel losing
its air charge. You need to depressurise the system to replace the
air, pressure needs to be set as manufacturer recommends, usually
around 1 to 1.5bar

If this fixes it but the problem recurrs after a while. you need a new
expansion vessel, the diaphragm inside is ruptured/leaking.
This can be checkedby removing itand trying to charge it with air. If
it won't hold a charge it is buggered.

Also search for other leaks.

Question. Does the sytem hold pressure when not used, ie cold?

There is another option, it may not be air but hydrogen, the by
product of anerobic oxidation.
Metals in the system take oxygen out of the water leaving hydrogen.
This can be resolved by adding corrosion inhibitors to the water.
This is more likely if you live in a hard water area.

You can test for this by seeing if the "air" you get out of the system
burns by applying a light to it. Obviously becareful, it burns with a
very hot colourless flame.