"Jonathan" wrote in message
ups.com...

I heard some bloke at an energy efficiency
company advising people to turn their boiler
control UP (leaving their room and cylinder stats
alone). ie: If the switch on the boiler went 1-6
and it was at 3, turn it to 4 or 4.5.

He said this is because the boiler gets
hotter quicker, heats the tank
quicker, and reduces cycling. Thus saving
energy. But won't this mess with the
condensing point of a condensing boiler?

During DHW is stored at high temperatures and at kleast 60C for the
prvention of legionella. When re-heating the boier temperature has to be
hot. You can't get away from it. Condnesing boier or not it has to be hot.
The only boier know that condenses wt all tiomes when supplying DHW is the
ACV Heatmaster, which has a unique combied tank-in-tank/boiler. A class act.

His argument is: tank calls for heat, boiler and pump start, boiler
reaches temp and turns off, tank still wants heat, pump still goes,
primary side water and boiler cool, hence the waste.

The heat exchanger has to take all of the boilers output. The best heat
exchange is a plate heat exchanger and bronze pump using a direct cylinder
Works out cheaper than a cylinder with a quick recovery coil in many cases.
Glow Worm in their new Extramax and Ultramax boilers use this method to
reheat an integral unvented cylinder. These plates extract so much heat
from the boiler it can really lower the return temperature to condensing
levels for most of re-heat time.

He is generally right. But, the cylinder coil has to take the boilers
output. On re-heating from cold a Part L cylinder will take the output of
the average boiler when set to 80C for the initial part of the re-heat,
until the return temperature is raised.

The problem is having the boiler at the ideal temperaure for CH to promote
condesning efficiency. An outside weather compensator can do this. Boilers
are available that will re-heat water at full belt and switch to weather
compensation on CH. Even so external waether compensators and the odd reply
can do this too.

It all just doesn't quite sound right, somehow!

The best is a heat bank in which the bottom CH half is heated by a weather
compensator. The boiler operates in a superior full flow through the heat
exchanger hydraulic environment, as does the CH circuit too. Boilers last
far longer when heating heat banks.