"Derek Geldard" wrote in message
...
On Fri, 25 Sep 2009 01:17:32 -0700 (PDT), Matty F
wrote:

On Sep 25, 7:39 pm, "Man at B&Q" wrote:
On Sep 25, 1:35 am, Matty F wrote:

We tend not to have header tanks here. I've only ever seen one, and
only because I was fixing it after a tradesman had failed. I don't
understand the need for them, since there are better and cheaper ways
of getting the pressure right.

They're not about getting the pressure right.

What are they for? Breeding mosquitoes and cockroaches and rats?
Putting lots of weight on the ceiling so it collapses?

Originally they were part and parcel of solid fuel (typically
fireback) boilers in a hot water system.

The fire/boiler held a big reservoirlot of stored heat. For safe
operation of the boiler to avoid a steam explosion a big reservoir of
stored cold water was required.

I've done away with ours, if I regret it a bit. The supply incoming to
the 1976 house is too feeble.

Derek


The water in all central heating systems is circulated by a pump. It has nothing
to do with mains pressure. In open systems the water in the radiators, central heating
boiler, and header tank is the same water constantly circulating around. (As it is in
sealed systems which have integral expansion tanks) When it expands it goes back into
the header tank and when it cools down its fed from the header tank. Any evaporation
from the header tank is compenasted for by a trickle from a ball valve. The header
tank should also be fitted with an overflow.

The water in the hot water system i.e the hot taps is totally separate.


michael adams

....


, and is just circulated repeatedly around your CH system.

The water in the central heating system is totally separate. It can either be a sealed
system with an overflow tank as part of the
system, or initially filled from the main including the header tank.