On Dec 19, 10:13*am, "dennis@home"
wrote:
"Dave Liquorice" wrote in message

ll.co.uk...

The radiators/remainder of heating system needs a constant pressure.

Why?

Because the water will flow faster and faster through the remaining path.
If you are unlucky it will make it noisy.
It also results in a lower temperature drop across the radiator, which makes
condensing operation more difficult and wastes energy.
An alternative is a variable head pump that slows down.

IMO the "you must have a radiator always on" is just because of the
inadequate control systems fitted.
If you only have one room stat then you lose all control if the radiator can
be turned off by another means.
If you turn the radiator off the heating will run when it isn't needed.

I think the "always have a radiator on" myth comes from the days of
solid fuel boilers when there always had to be a convection heat sink
to stop overheating if a control problem/pump failure arose.