On Jan 18, 3:59*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

Vic has it right. Any air in the system will be picked up by passing
water. The water will then release this air at the point of least
pressure. This is usually at the highest/farthest radiator. Rich
Trethewey gave a great explanation of this on one episode of TOH. A
simple explanation is that water will boil more vigorously in a pot
with the lid removed than a pot with a lid on.

You need to bleed every radiator in the system until all air is gone.
I usually do this first with the system off then run the pump(s) for a
while then shut down and bleed again. In a big system like you have
it can take a long time but you will eventually get all of the air
out. Then you just have to keep the pressure high enough to prevent
the new water from releasing air again.