Water tank in loft

grumbler

Bendy_House said:

Hmm, I see a flaw...

Yes, there is no flow, and yes you can imply that - by this - there is no pressure. But what there is, is an effective 'block' caused by the bubble, and beyond this bubble is cold water backed by the same pressure as the hot water at that level.

If there is a 'bubble' (big enough to stop the water flowing), then the pressure can't be the same. The pressure is created only by the parts filled with water and some parts (H2 in the picture) even create negative pressure.

In the picture H1=H2, i.e. two parts balance each other making the total pressure below zero.

Ok - idea; this is risk-free Attach the hose (even worth buying a spout adaptor for this), and unravel the hose in as straight a manner as you can downstairs and out the door. Turn on the 'hot' tap only, and let it run until water is coming out solidly from the hose end - no splutters. Ok, now also open the cold tap fully, and then shut off the hot.

This may work.

Or connect the hose to both the kitchen/outdoor tap and the tap in the bathroom and use mains pressure to force the possible bubble up.