Kospel PPE 15 kW - hot / lukewarm water even at the maximum power setting.

Hello,

From the news I have a problem getting warm, hot tap water. The stove switches on correctly and, depending on the temperature control, successive LEDs light up on the control board (6 red ones), however the sixth LED for max flashes always, never illuminates. Water is often "lukewarm warm".
I cleaned the device without any effects. The only solution where the temperature is satisfactory for a warm shower is to change the switches (6 positions) to the ON position (according to the instructions for the furnace power 6.75kW). Now the temperature is satisfactory, hot at the middle level of the regulator and the red diodes glow with a constant light (by reducing the temperature they react by extinguishing the last). The stove turns on and off properly.
Is there any threat to this configuration? Does this indicate a falling heating unit or a weaker heater fitted than specified?

I would start by checking the electrical installation, namely the voltage between phases.

Hello,

I measured the voltage between phases and neutral and for each phase is 234V.
Between phases (stove in standby mode) the voltage is 403 V for each possibility.
When the stove is turned on to the max, the voltage between the phases is 400 V.

On setting the switch on the control board (3 and 4 and 6 to ON) for 15 kW, the water is at most lukewarm.
On setting all positions on the plate (from 2 to 6 to ON), i.e. for 7 kW, the water is even very hot at MAX.

I wonder about the safety considerations of such a solution (short circuit, burning of heaters, system, savings).
Which defective item does this case indicate?

Tension is not everything. The next stage is the measurement of current from individual phases at max load. It should be as in the table in the instructions. Lower values indicate the failure of the heaters. If the currents match, we go to the water flow in the tap. 15 KW is not crazy and you need to ensure that the water flow from the tap does not exceed the value given in the table under "performance". The pressure on the network is set to 3.5-4 bars max. If these 15 KW is to increase the water temperature by 40 degrees at a flow of max 5.5 l / min, it can be seen that it is suitable for washing hands and dishes, but not for filling the bathtub. If the measurements show that the device is operational, then often the restriction of water flow takes care of the temperature. The question of efficiency remains because here expectations are usually much higher.
Regarding "security reasons". Measure currents at 15 and 7 KW. Physics can't be fooled. Heats harder - takes more. And this is not just about the heater but also about the electrical installation. premises.

The predecessor wrote well. This power is always less than the power of a gas stove (Junkers are usually 19.2 kW or 23.6kW) and if you want to get a large flow (strong stream in the shower) then the water will only be warm (without cold admixture) and if cold water is " ice cold ", hot water can be barely warm. If the water temperature increase is 40 degrees at a flow of 5.5 l / min, then at 11 l / min. would be 20 degrees. That is, when cold water is 15 degrees, it would be 35 warm, but when cold water is 10, then the warm water at this flow will be 30 degrees. In mountainous regions, cold water can be even colder (sometimes in the middle of winter it can be only 5 degrees). That's how it is with electric instantaneous water heaters. If they had the same efficiency as gas, they would have to have very high power, and electrical installations are usually not adapted to this.

Unfortunately I have no way to check the current because my meter is up to 20A (Benning MM-3).
It is interesting that on the 15 kW setting, even on the maximum setting, the sixth red diode always blinked on the control board.
For 7 kW, all LEDs light up continuously at the maximum setting and the water for the same water flow is very warm and for 15 kw lukewarm.

What does the control change?

Maybe the power supply does not withstand such a heavy load and there are voltage drops. It is worth observing whether during the operation of heating the bulbs (but ordinary, not compact, not LED) they start to shine darker than usual. If so, there is an evident voltage drop (this is a common phenomenon, e.g. when I switch on an electric kettle on a plot, the light immediately shines fainter). It's just that this bulb (for control) should be connected to the same circuit.