AFAIK there is no active control of the flow rate by the boiler. The DHW
temperature knob (always stuck immovable IME) is simply a flow restrictor:
the less flow the grater the temperature rise.



--
Ed Sirett - Property maintainer and registered gas fitter.


Funnily enough the DHW temperature knob on my now junked VCW242
was stuck immovable!

BTW my installation of a Vaillant Turbomax 828 to replace it went OK,
thanks to all those on this board who helped with my queries. The worst bit
was getting the pipes through the cavity wall ( moved the new boiler to an
outside loo location ).

Worst screw up was finding out the hard way that a single drop of
water left in a system when fitting solder joints will screw up any chance
of getting a sound joint.

Second worst screw up was not realising that mild flux and end-flow
fittings do not work well together. I thought that brightening the copper
end of the pipe with wire wool would obviate any problems, but it turned
out ( obvious really ) that you needed to brighten the inside of the copper
fitting as well! I eventually used a much more active flux ( Everflux ) and
abraded any copper surface which was going to have solder flowing
over it.

Andy