Air in ch system

[someonelse]

I can always hear air rushing around the system.

Bleeding rads doesn't help - only water comes out.
New hw cylinder several years ago & a bleed valve added: virticle pipe next to the cylinder with bleed valve at top. Only water comes out.
Ball valve cleaned/working in tank in attic. Always 2/3 full.

It's an old 9mm microbore system though all rads and boiler replaced over last 10 years.

Any ideas or shall I just not worry carry on living with it?

 

[John506]

Do you have a pump?

Try bleeding the last radiator on the system, this may be the one with air in.

Go up into the loft, with a peice of paper, and hold it flat on your hand under the vent pipe (the one that bends over the cistern) about an inch away and get someone to turn the CH on. If the paper rises to the vent pipe, i.e air is being sucked in from the vent pipe, post back with the position of the pump on the pipework.

i.e before or after the vent pipe, measurements from the vent to the pump etc.

 

[someonelse]

Thanks. Tried the paper on the vent test. No air suction.

Yes there's a pump (in airing cupboard below vent in attic) but not clear which pipe it's on - before or after vent.

Can't bleed "last rad on the system" as.... there IS no last rad! The old microbore system is designed with about 12 - 15 pipes coming from a manifold near the pump, each pipe feeding an individual rad!

Have tried switching pump from '2' to '1' (I didn't realise till today it has 3 settings.) Noise seems less, and rads still seem to get hot, so I gues at the least I'll be saving on the leccy bill!

Is there a formular for which setting pump should be on? I'm guessing if it's on 3, water circulates faster, so stays in rads less time, so returns to boiler hotter, whereas on 1 it circulates slower, stays longer in rads and heats rooms more eficiently.....?

 

[John506]

Not so much a formula, just first off set it to lowest settings, if your central heating heats up quick enough then leave it at that, if not, switch it to speed 2 and so on and so fourth.