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 at
http://www​.makewrite​.demon.co.​uk/SealedC​H.html
but still none the wiser.

Thanks in advance,
Rob.