I am having problems with my underfloor heating manifold in that everytime I start up the heating all I can hear is air rushing around the mainifold. I have auto bleed valves on the manifold but it doesn't seem to be doing the trick. I have 2 bleeds up in the loft for the flow and return to the manifold but they never need bleeding and always throw out water when checked.
I have turned off all the heating circuits from the manifold and the air noise remains the same.

wallymotors, October 2009

When i said everything is turned off what i mean is that the manifold is still on and pumping water but I have closed the actuator valves so the room circuits are closed. Water just passes through the mainifold and back to the boiler /pump.
The system is a combi boiler
Thanks

wallymotors, October 2009

if you have turned off the heating and you still can hear air sound like it is some were else, is it a pressure system or tank feed?.

erj, October 2009