Air Blockage Downstairs Rad

[kestrel]

Help required please.....
I have a downstairs radiator running only slightly warm when heating system is on.
I think I have a air blockage on the return pipe, from the downstairs radiator, as this is cold as it rises up the wall??????????????????.
The feed pipe is hot as normal???.
I have a drain down valve under this radiator and have been told that I can connect the hose from mains water supply to move the air blockage??.
Are there any extra precautions I should take before commencing with this procedure and how much water should I feed into system.
What are the implications and any faults with doing this?.
Its a conventional standard open vented system with boiler and pump with header tank in loft.
Many thanks....

 

[bathjobby]

Assuming you have tried to bleed this rad and have bled all other points, rads, pump, etc....
Firstly open both valves on the rad wide open (this may clear it but probably not). Make sure the hose is filled with water before connecting to drain cock (don't want to push any more air into system). connect to drain and open drain valve. what you want is a lot of pressure but for only a short time e.g. 3 or 4 second burts (this is going to go to the F/E tank so you don't want that overflowing) so get someone to open hose tap fully and quickly, then close, having first used a hoseclip in the drain connection and have it tended. Hopefully this will result in lots of gurgling as system refills. If not, repeat, but in between each try go and check the level of water accumulating in the small feed and expansion tank and if need be, bale some out between tries. When cleared, don't forget a final bale out of F/E tank.

 

[Polly1]

I dealt with an air block for a friend myself last week & managed to flush it through simply by turning off one valve on every other radiator to get enough pump pressure from the boiler feeding to the one that wasn't heating.

This flushed the airlock through quick smart (loads of bubbling as it shifted). It was job done in 10 mins & the rad has been great since. You may want to try this if you haven't already.

 

[kestrel]

All,
Many thanks for your replies.
Have investigated it slightly further since then.
It seems to be drawing air in from the header tank overflow pipe?.
If I go into the loft there seems a intermittent sucking pressure on the overflow pipe.
Intermittently as though its short of water in the system when warming water to correct temp
Overflow tank feed and pipe has enough clean treated water in it, as I cleaned this out last year and ran fine..
Also if I switch the immersion side of heating off it seems to alleviate the noise somewhat.
Would this indicate air, on immersion side of system is primary cause.?
Also would a surge of water clear this as well?.
Would appreciate your thoughts?.