Yesterday we installed a 3 liter instant water heater which uses 3 KW. After the install, hot water is coming through the tap, albeit very slowly. The cold water is coming fast. Our geyser was installed by an electrician who told us that instant geysers do not require pressure. How can I get the hot water to flow quickly?

  • I am very confused as to whether this is a tanked or tankless hot water heater. If tankless, the 3-litre figure makes no sense, unless it's 3 litres/minute (a slow rate, and a tick slow for a 3000W heater unless the goal is to make water hot enough for tea). If tanked, 3000W seems rather excessively large for a 3-litre tank. Commented Mar 5, 2017 at 19:22
  • Googling 3kw 3 litre geyser reveals this is an Indian idiom: probably a "Flora", which sells for R2800 or about US$42. I don't know how Indian labor or market protectionism works, but Americans wouldn't expect much at that price. It seems to be marketed for bathing, offering a quick recovery time (true) so the whole family can bathe. All this tends to suggest it is a tanked heater. Commented Mar 5, 2017 at 19:40
  • 3kw instant hot water to me would mean tankless and that is quite small. Of the point of use tankless electrics I have installed the units thermostat reduces the flow to keep the water warm, if you increase the flow the water will be cold or cooler the only way to increase the flow would be to reduce the temp setting or get a larger unit.
    – Ed Beal
    Commented Mar 19, 2018 at 13:39

2 Answers 2


30°C temp raise (10°C to 40°C) for 1L/min requires about 2,1kW of power. So with a 3kW POU you can't expect a big flow. An 'adequate' shower consists in about 6L/min. These are the numbers. Especially if main water is cold, instant POU are not enough, better to install a under-sink tanked heater (10L), it delivers much better flow even at higher temperatures.


Electric 'point-of-use' hot water heaters have a water flow rate much less than the cold water line. The behaviour you describe may be normal operation for this unit.

Is this unit being used for a shower or to heat water for the kitchen sink faucet for dish washing?

From this unit one could get a small amount of very hot water on demand and by mixing with cold get a low volume stream of barely warm water which would last several minutes, until the 3 L of very hot water in the mini tank was used up, then the water would go cold and one would have to stop the flow for maybe 10 or 15 min until the water in the tank got hot again. It seems that this unit is what is called in the US a 'mini tank'; the water in the tank will be very hot (~>60 C), but will not have a high flow rate.

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