"Kev Parkin" wrote in message
om...
I recently moved into a house with a gravity fed CH system, the Baxi
back boiler is 4-5 years old but the heating system looks much older,
each rad (except the one in the bathroom) has a thermostatic valve and
there is one room stat in the hall.

As everyone knows, with this type of system it is not possible to run
the heating without the hot water.

My problem is that I have been running the heating on "constant" over
the weekend and as a result the hot water is scalding hot to the point
where steam and water have been jetting into the header tank - my loft
sounds like the local branch of Starbucks and the wooshing and banging
is not only getting on my wick but I'm sure it's not doing the system
any good.

I recently replaced the ballcock on the header tank as this kept
overflowing, it still overflows so I guess it's the hot water cylinder
that's up the chute! and I will have to replace this.

At the same time I am considering modifying the system so that the
heating can be run independant of the hot water and maybe zoning the
upstairs and downstairs.

I would like to ask if anyone has anyone undertaken this (or a
similar)job and if they have any tips/tricks/do's dont's/information
on parts/suppliers etc that may help me decide the best way to do
this.

Thanks in advance,

Kev

The simplest way of controlling the hot water - short of converting to a
fully pumped system - is to put a zone valve in the gravity circuit. Control
this with a cylinder stat, and use the voltage-free change-over contacts on
the zone valve to contol the boiler. If you have a look at the C-plan
details in
http://content.honeywell.com/uk/homes/systems.htm you'll get the idea.

[It took me a few minutes to suss out the wiring - but I believe that it
works like this:
Hot water only: The zone valve is open, the boiler runs but the pump
doesn't. As soon as the hot water demand is satisfied, the valve closes and
the boiler stops.
Heating only: The zone valve is closed. The boiler and pump run whenever the
room stat is calling for heat.
Both together: The zone valve is open. The boiler and pump both run. When
one of the stats is satisfied, it operates as per HW or CH only (as
appropriate) and when both are satisfied, it shuts down completely.]

This would certainly allow you to have CH all day without red-hot HW.

If you go go this way, be careful where you position the zone valve - to
make sure that there is always a clear path between the boiler and the
expansion tank.

Roger