"Andy Hall" wrote in message
...
On Fri, 17 Jun 2005 16:37:19 +0100, "TheScullster"
wrote:

BigWallop

That would mean major piping works!
As the modern boilers modulate, is the
2 boiler approach justified (other
than by the "only one service is lost in
the event of failure" argument).

For the scenario that you describe,
stored HW is a much better option.
You may wish to upgrade the cylinder
to a fast recovery type.

Nor so. The cheapest option, which will give greater longevity and save
space and never runs out of hot water, is one of the new Japanese 2 bathroom
instant hot water high flow multi-points. The Rinnai is "very" reliable, and
is sold all over the world. Rinnai are the world's largest gas appliance
maker, with typical Japanese quality.

A 29kW system boiler will cost about £775 (Glow Worm 30kW system boiler)
250 litre unvented cylinder complete with valves is: £1404 inc all valves.
Which is £2179.

A Rinnai 32E which saves space as no cylinder, and gives around 25-26
litres/min and does two bathrooms, and NEVER runs out of hot water, and can
be fitted outside is £863 and £124 for an external guard and the Glow Worm
to heat the CH at £775, is a total of: £1762. £417 cheaper.

The Rinnai will outlast the unvented cylinder and cannot explode causing
catastrophic damage. It is best to fit a flow switch on the cold supply to
the Rinnai to switch off the Glow Worm CH boiler to keep gas consumption
within a U6 domestic meter. Wire it in the stat/programmer circuit in
series. When DHW is called (hot tap on) the CH boiler is switched off.

This by far the best solution.