Instantaneous Water Heaters

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?

Reply to
Grumps
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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.

Reply to
Chris Hogg

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

Reply to
Tim Watts

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

Reply to
Harry Bloomfield

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.

Reply to
Roger Mills

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.

Reply to
Adam Funk

We used to have a very variable pressure water supply, especially in the summer. We're at the end of about half a mile of blind run of supply pipe, and halfway along there's an offtake to a holiday park. Mornings and evenings the pressure would fluctuate wildly as the holidaymakers went about their ablutions. Unlike your system, our shower didn't have a low pressure heater cut-off, or if it did, it didn't work, so if you were showering when the pressure suddenly dropped, you had to be pretty nippy to get out of the shower before you were scalded. Thing of the past now thank goodness, as we have a pumped shower supplied by the DHW and CW tanks.

Reply to
Chris Hogg

No.

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.

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

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.

Reply to
John Rumm

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.

Reply to
Andrew Gabriel

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