water leaking from expansion tank but not from ballcock ?

[Bob4u50]

I am experiencing problems with my central heating system as follows :- My upstairs radiators only get warm but downstairs they are hot !
Every time that i bleed the radiators, the expansion tank overfills and leaks water out of the overflow pipe. The additional water in the expansion tank is NOT coming from the ballcock feed, but it is coming from the outlet pipe of the expansion tank (getting feedback) causing the water level to rise above the ballcock float and escape out of the overflow piep ? Can anybody suggest a remedy ?

Thanks

Bob

 

[oilman]

Is the pump turned off when you bleed the rads?

 

[Bob4u50]

Thanks for replying.
I think the system was on at the time, but I have tried it so many times now, I think it does the same with system off as well ?
I will try it again tonight with sytem off, then try again with system on and let you know later.

Thanks

Bob

 

[oilman]

You only need to bleed with the pump off, if it's on it can suck air in.

 

[Bob4u50]

Tonight I switched off system and let cool down.
Then vented rads on lower floor first (no air) then vented rads on upper floor (all had air except one) but all seemed to vent ok.
No water overflowed from expansion tank this time!
Then switched on and all rads seemed to heat up ok (except for 2 on lower floor) which were hot @ top and cold @ bottom, but heated up ok later.
Therefore so far, so good !
Obviously I had been venting before with system on all the time (DOH !)
Will come back if any further problems.

Thanks for your help.

Bob