Rads not heating up & constantly getting air in system

[BOBH]

Can anyone suggest why 2 or 3 of my rads are not getting hot?
The feed to a downstairs rad is hot but the rad is not warming up, I have checked that the feed valve is fully open and have opened up the return valve ?
Another radiator upstairs is also cold. I have removed this rad, flushed it out and replaced new valves, but it is still cold and the feed pipe sometimes gets hot and another time does not ?
Plus most of my upstairs rads keep getting air in them, I can bleed them all one day and by the next day there is air present again ?
I have bled the pump but still having problems ?
Appreciate your help.

Thanks

 

[brumylad]

The air might be hydrogen produced by corrosion if inhibitor has not been used after all that work you did on the system.

Sounds like a balancing problem. turn off all the rads apart from those not getting hot.

 

[BOBH]

Thanks for your advice.
Will try balancing first and then deal with air problem.

Thanks

 

[kevplumb]

ongoing problem or recent ?

 

[BOBH]

problem seems to have occurred since heating turned back on after this summer.

 

[kevplumb]

have you checked the head tank ?

 

[BOBH]

BY THE HEAD TANK I ASSUME YOU MEAN THE EXPANSION TANK IN THE LOFT ? IF SO, I CHECKED THIS LAST NIGHT AND FOUND BALLCOCK TO BE OPERATING OK, AND EXPANSION PIPE IS CLEAR APROX 2" ABOVE WATER LEVEL.

 

[kevplumb]

1 dont shout
2 its the obvious that gets missed
3 could be the pump drawing air down the vent
4 just cos the tank is full it dosent mean its getting into the system

 

[BOBH]

1 SORRY IF U THINK I'M SHOUTING (COS I'M NOT)
2 I AGREE, AND I MISS MORE THAN MOST.
3 HOW DO I CHECK THAT PUMP IS NOT DRAWING AIR DOWN THE VENT ?
4 I SEE WHAT U ARE SAYING, BUT WHEN I DRAIN THE SYSTEM DOWN, IT
APPEARS TO REFILL WITHOUT ANY PROBLEM AND ALL RADIATORS FILL
UP OK !

THANKS

 

[PEDANTICVINDICTIVEMAN]

If the system has worked ok in the past and been installed correctly then
try draining some water from the heating via a downstairs drain point and check to see if the ballvalve starts to fill in the expansion tank, this will tell you if the cold feed to the heating is blocked or not, if you can empty the system and the tank stays full it means the cold feed is blocked, this will cause the pump to draw air down the vent pipe and oxygenate the system, if so you will need to find the blockage, most likely place is where the cold feed tees into the system.

 

[kevplumb]

and turn caps lock off

 

[PEDANTICVINDICTIVEMAN]

SORRY, WHAT WAS THAT, NOW LISTEN, I SAID I WANTED A ROOM WITH A VEIW, THE RADIO DOESN'T WORK AND THE BATHS TOO SMALL, WHAT, YOUR FAWLTY, WHO'S FAWLTY, KE SI, SI KE, WHAT,NOW LISTEN !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[kevplumb]

ok shot pedantic

 

[BOBH]

sorry about caps lock

 

[croydoncorgi]

Maybe better to get rid of the airleak first. From the rate you say the air is building up in the rads, it must be air, not hydrogen.
Check that the stem seal glands on the water pump valve on the suction side of the pump is not letting air in, then work back along the return pipe checking rad valve glands and any other place air might be getting in. Somewhere between the pump suction side and the 'middle' of your system, suction turns to pressure (because the pump pushes as well as pulls!).

Once you are no longer getting air in the system, the reason for other problems may become clearer.