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?

On 15/05/16 15:43, Chris Hogg wrote:
On Sun, 15 May 2016 15:12:07 +0100, 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?

I don't know about kitchen water heaters, or about the more
sophisticated shower heaters, but the simpler electric showers have
one, sometimes two, heater elements that run at full power all the
time. Water temperature is varied simply by varying the flow rate. Hot
shower - slow flow rate, cool shower, faster flow rate, or switch off
one of the heaters. Very unsophisticated.


Mine (inline water heater) has power regulation, so it will hold the
temperature until the flow gets too high - then you get cooler output.

Tim Watts a écrit :
On 15/05/16 15:43, Chris Hogg wrote:
On Sun, 15 May 2016 15:12:07 +0100, 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?

I don't know about kitchen water heaters, or about the more
sophisticated shower heaters, but the simpler electric showers have
one, sometimes two, heater elements that run at full power all the
time. Water temperature is varied simply by varying the flow rate. Hot
shower - slow flow rate, cool shower, faster flow rate, or switch off
one of the heaters. Very unsophisticated.


Mine (inline water heater) has power regulation, so it will hold the
temperature until the flow gets too high - then you get cooler output.

Mine is able to adjust both flow rate and modulate the power to achieve
your set temperature.

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
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On 2016-05-15, Chris Hogg wrote:

I don't know about kitchen water heaters, or about the more
sophisticated shower heaters, but the simpler electric showers have
one, sometimes two, heater elements that run at full power all the
time. Water temperature is varied simply by varying the flow rate. Hot
shower - slow flow rate, cool shower, faster flow rate, or switch off
one of the heaters. Very unsophisticated.

The electric showers that I have had worked that way, with the fun
side effect that drops in water pressure (taps opening all the way,
toilet flushing) can affect the output temperature, sometimes enough
to cause the "not enough pressure" sensor to kick in & cut the heating
element off. Fun.

AIUI, better electric showers are now available, but I don't know how
widespread or comparatively expensive they are.

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?

No.

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.

Don't assume the unit will actually have a flow regulator - many don't -
draw water too fast and the temperature will fall. The set temp is only
an upper limit.

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.

To which you will mix in some cold as well to achieve the desired
temperature.

Does this have any effect
on the shower head flow or does the shower thermostatic mixer handle it
all?

Ideally you want the boiler temp set to a sensible maximum - however
depending on how sophisticated the boilers control system and also
whether it can modulate the burner power, it may make more sense to set
it higher rather than lower. A constant (lower) flow of very hot water
can be mixed down at point of use.

Set the heater temp too low, and you may find it cycles the burner on
and off to prevent it exceeding the set limit temperature. Not ideal for
a shower, since it sill swing between hot and cold.


--
Cheers,

John.

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In article ,
Grumps writes:
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?

To add to the other comments...

You should use a thermostatic shower mixer designed for multi-point
water heater and combi use. These are very fast acting, but sadly
more expensive than the cheap wax pellet type. They also know they
cannot vary the temperature by controlling the hot flow rate
(reducing the hot flow rate will just produce hotter water to
cancel out the change). They will also handle high pressure cold
with widely varying pressure hot (as is common with instant water
heating when someone else turns on/off a tap), and protect against
use with too low cold water pressure to be able to prevent scalding.

I've had a Gainsborough one for ~15 years, and it works very well.
Used to try and use a manual mixer before, and it was extremely
difficult to adjust the temperature, and a disaster is the washing
machine decided to start drawing water halfway through a shower.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]