Upstairs rads need constaint bleeding

[plumb1]

Hi can any one shed light on my problem, I have replaced 8 of the 11 radiators in my victorian house ready for a new boiler next year (boiler working fine at the moment but old)
I have bled the radiators and all was fine for couple of weeks the I noticed a some of the upstaires rads are cold or warm I bled them again and have been bleeding them each night for a week a lot of air is released each time and I can hear the water and air in the rads.
I have no leaks but air must be entering the system somehow?

my boiler is 30 years old, but working fine, the expansion tank overflows sometimes I have no problem with hot water and the downstairs rads are very hot when the heating is on

Its driving me nuts bleeding the rads every night

Please Help!!!!!!!

 

[seco services]

maybe drawing in air down the vent pipe.

 

[Bonesy60]

easy to test get a pint glass of water and put the end of the vent pipe into it if water gets sucked in then thats your problem have you changed the pump recently.

 

[bengasman]

was there a lot of sludge when you changed the rads?

 

[75pete]

See FAQ 47 "over pumping"

 

[namsag]

Bleed it with the heating OFF. as you can make the problem worse on some systems by bleeding it with the pump on

 

[plumb1]

Thanks namsag,

I was taught to bleed with the heating on so the water pumps round,

I have bled the rads and no overflow from the expansion tank. i have put the heating back on and waiting to see what happends.

 

[D_Hailsham]

I was taught to bleed with the heating on so the water pumps round

I would have thought that was the last thing you wanted!

If the water is being pumped round the circuit when you open the bleed valve you will get an almost instantaneous jet of water shooting out of the bleed valve and won't have the foggiest idea if there was any air in the rad or if it has all been removed.

If you bleed with the pump off (preferably with the water cold) and there is any air in the rad, there will be a delay between opening the bleed valve and the water slowly coming out. This makes it easier to know if there was any air in the rad.