"IMM" wrote in message
...
"EMC" wrote in message
...
IMM,

Thanks for the information. By throw-over valve,
do you mean a diverter valve?

Yes, that is the correct terminology.

I assume that by using this arrangement
all hot water from the boiler will be diverted
to the cylinder when demanded. If several baths,
washing machine and shower are used
in succession (probably unlikely I
know), would that mean the radiators may
not be supplied for some time?

Yes, but in reality the cylinder is re-heated pronto. The cylinder will be
well re-heated and well into CH mode by the time another bath is run. A
largish boiler may be re-heating the cylinder faster than what the shower
can draw-off the hot water.

As you are buying a new boiler, look at getting a combi to supply the
showers only. Then no expensive, noisy, vibrating, troublesome power
shower
pumps. Have the CH section as a conventional system with a 3-way diverter
valve. As the combi's water section will only be used for showers, once
or
twice a day, they last quite a time. All the water system, except the
showers will be at low pressure and high flow.

If you are replacing the cold water tank think about a "combi cylinder".
Have a 50-50 split of hot water and cold water storage. Have the cold
water
section 115 litres and take all the cold supplies off the cold water
section. This way using a combi boiler for the shower side you eliminate
the cold water tank in the loft, or put the combi cylinder in the loft
(well
insulated of course) and have a larger airing cupboard. Telford do the
Trident, which has a 115litre/115litre split. have a look at their web
site. Combi cylinders are simpler and quicker to install.
http://www.telford-group.com/trident.htm Some cylinder makers will
provide
combi cylinders to order, in that if you wanted a 115 litre hot section
and
115 litre cold section and appropriate tappings, etc, they will provide
it.

So you would have:

1. A combi boiler supplying any high pressure showers.
2. A combi cylinder with a large cold water section. providing low
pressur
hot and cold water.
3. A DHW priority system.


On the subject of quick recovery
cylinders, what is Part L?

In April part L of the building regs came into being. It implemented
energy
regs to water and heating systems. Part L cylinders means that all
cylinder
must take no more than 30 minutes to heat up. This obviously is
depending
on the boiler temp being on max, which it should be, and the flow through
the coil. Quick recovery are far superior to Part L cylinder. So, in a
plumbing shop the man may say these are all quick re-heat because they all
conform to Part L. I have heard that being said by counter men.

I am also considering an unvented cylinder
and a sealed system boiler. Which unvented
cylinders would you recommend as quick recovery?

An unvented cylinder needs to be fitted by a BBA approved fitter. They
are
not DIYable. Consider the suggestion I made above, which is cheap and
easy
and give lots of flow and high pressure showers. Otherwise fit a heat
bank,
rather than an unvented cylinder which requires large bore blow-off pipes
to
outside, tundishes, etc. Some heat banks don't even require overflows.

A sealed system boiler is fine. But many combi's are cheaper and you get
the
high pressure DHW section for showers for free and a very high output that
modulates. Many wise installers buy cheap combi's and ignore the DHW
section, just connecting it to the mains and capping the hot water
draw-off
pipe off.

When fitting a new boiler to an existing system always insert a strainer
on
the return next to the boiler to catch ant crud floating around. In fact
some Alpha combi's have a cyclone in the return pipe inside the boiler to
catch the debris.

Heat banks:
http://www.heatweb.com
Also from Range cylinders under "thermal storage" on their web site. Albion
don't do heat banks.



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.488 / Virus Database: 287 - Release Date: 05/06/2003