On 15/05/2016 15:12, Grumps wrote:
I think I'm being a bit stupid, but I can't work out the operation of
these units.
If you have a instantaneous gas water heater do you have to keep
changing the unit's set temperature when you want to fill a kitchen sink
or have a shower?
For a kitchen sink the temp could be 50C, so you set the heater to 50C
and that should be the max you get, but the flow rate would be limited
depending upon the heater's power.
But if you want a shower, if you leave the dial at 50C then the flow
will be lower than when it's set to (say) 40C. Does this have any effect
on the shower head flow or does the shower thermostatic mixer handle it
all?

If you want water to come out of the shower head at 40C, and you want
the highest flow rate you can get at that temperature, there are various
ways of achieving that. For example, you could run the heater at 40C and
adjust the flow such that it *just* achieves that. OR you could run the
heater at a (lower) flow rate which just achieves 50C, and mix its
output with cold to get a mixed temperature of 40C at the shower head.
You'll get the *same* flow from the shower at 40C by either means.

What is important is that you keep the heater running flat out. If you
allow it to modulate its power, you'll get a lower overall flow rate.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.