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Tech support

Online support - rainwater harvesting system operation checks and corrections

If you’re still experiencing any problems, please contact our technical support team via or give them a call on 01404 540745(available from 8am to 5pm, Monday to Friday).

1. Check the operation mode of the system by viewing the visual display and the indicator lights of the control unit. The system has 3 operation modes

i) Automatic operation drawing rainwater from the underground tank
Text: Reservoir mode (Zisternenbetrieb)
Lights: Operation (Betrieb) light green
Notes: Visual display will also show depth of rainwater in cm

ii) Automatic operation drawing mains water

Text: Drinking water (Trinkwasserbetr)
Lights: Operation (Betrieb) light green, MWO auto (TWN auto) light yellow
Notes: Not sufficient rainwater inside RWH tank, system draws mains water from break tank

iii) Automatic operation drawing rainwater from the underground tank
Text: Drinking water (Trinkwasserbetr)
Lights: Operation (Betrieb) light green, MWO manual (TWN manuell) light yellow
Notes: User has switched system to manual mode drawing water from the mains

To turn on the manual mode press the ‘ON’ (EIN) button, to turn off the manual mode, press the ‘OFF’ (AUS) button.

The water exchange allows the mains water in the tank to be refreshed and prevent stagnation. This is an automatic operation whereby the system draws mains water for a short period of time.

Text: Drinking water (Trinkwasserbetr)
Lights: Water exchange (Wasserwechsel) light yellow
Notes: Continues until the 9 litres in the break tank is used and replaced from the mains

2. Measure the depth of rainwater available inside the tank. Does this correspond to the cm value recorded on the visual display of the control panel?

If the control unit shows the rainwater depth as a percentage, convert back to cm by pressing and holding both the ‘ON’ (EIN) and ‘OFF’ (AUS) buttons together until an audible click is heard.

If the control unit does not show the correct rainwater depth, then:

  • Check the junction box in the RWH periscope for signs of submergence. If the soakaway is insufficient, or blocked or the water table is very high the sensor junction box may become submerged. It is not watertight, so submergence will damage the operation.
  • Check the depth sensors are correctly installed as follows (any incorrect items should be remedied)
    – The blue sensor cable should pass through the right cable gland (front view) and connect to sensor terminal two. The black sensor cable should pass through the left cable gland and connect to sensor terminal one.
    – The sensor cables should be installed to ensure that the weights are located 5-10mm from the base of the RWH tank.
    – The sensor lines must be free from interference and must not; touch the wall, touch each other, be laid in a pipe, be knotted, be connected together, be damaged in any way.
    See page 20 of the installation manual for further details
  • Unplug and reconnect the sensor cable inside the control unit
  • Re-calibrate the depth sensors to the correct rainfall depth (see pages 14 and 15 of the installation manual for details).

3. If the control unit is in automatic operation and drawing mains water despite the control unit displaying the correct rainwater depth inside the tank then:

  • Check the depth at which the control unit is set to automatically convert from rainwater to mains water by entering the parameter menu and viewing parameter 2; ‘DWB Switch on’ (TWN – Einschaltpkt).

    A value in centimetres should be displayed. The factory set value of 20-25cm is recommended. If this value is too high, a significant volume of rainwater will remain inside the tank when the system starts to draw mains water. If this value is too low (5-10cm) the likelihood of the system drawing dirty water from the base of the tank will increase.

    See pages 8-11 of the User and Maintenance Guide for full details of how to check and alter the depth when switching to automatic mains water mode.

  • Check the hysteresis level (the additional depth of rainwater added to the rainwater tank before the control unit automatically converts from mains water mode back to rainwater mode). The factory set value of 2cm is recommended. If this value is too great, the amount of rainfall required for the system to automatically convert back to rainwater mode will be much higher resulting in a longer period drawing water from the mains.

    Example – If the auto mains switch over value is 25cm and the hysteresis value is 2cm, the control unit will switch back to rainwater mode when it records a rainwater depth of 27cm in the underground tank. The Hysteresis function is parameter 3 in the parameter menu; ‘DWB Hysteresis’ (TWN – Hysteresis). See pages 8-11 of the User and Maintenance Guide for full details and to alter the hysteresis value.

  • Check that parameter 5 (type of mains water operation) is set to ‘DWB Mode Cap. Sensor’ (TWN – Modus Kapazitivsensor). If set to either of the alternative two options (no mains water operation or conductance sensors) the system will not operate correctly. Capacity sensors are installed within the RWH system (option 2 of parameter 5).
  • For more details and to change the parameter see [ages 9-11 of the User and Maintenance Guide). iv) Ensure that there is no air in the pump or suction pipe. Operate the system in rainwater mode and open a tap supplied by the RWH system. The pump will start working. Press the red button on the pressure set until the sound changes and generates pressure itself (visible on the dial).

4. Further control unit check include:

  • Check that the system is plumbed correctly with the mains water connected to the left-hand side of the control unit, the rainwater suction pipe secured to the rearmost top connection and the discharge pipe (to taps/appliances etc) attached to the nearest top connection. Ensure that any isolation valves installed are open and allowing water flow.
  • Check that mains water is filling the internal 9 litre break tank by removing the yellow plastic lid on top the control unit and observing the system operation when in mains water mode.
  • Check to ensure that the float valve inside the break tank is not clashing with the casing and allowing entry of additional mains water. If a problem, reposition the float valve if possible or slightly unscrew the fasteners holding the control unit onto the wall to reduce any deformation caused by over tightening.

5. If necessary, restore the factory settings of the control unit as follows:

  • Turn off the power supply
  • Press and hold the ‘OFF’ (AUS) button
  • Turn on the power supply and continue to press the ‘OFF’ (AUS) button until an audible click is heard.
  • The visual display will show the following text; ‘Standard Param! Pls, acknowledge’ (Standard Param! Bitte quittieren).
  • Press the ‘RESET’ (QUIT) button to acknowledge the request to return to factory settings. If the quit button is not pressed, the return to default is not accepted. The control unit will return to its previous settings and resume working without adopting the default parameters.

6. Ensure that water can be drawn from the underground tank by ensuring the mesh filter on the end of the suction pipe is not blocked. Also check the non-return valve on the suction pipe to ensure it is installed in the correct orientation and check to see if it has become stuck. This could prevent rainwater from being drawn from the RWH tank.

  • Check all pipework for signs of leaks and correct any found.
  • Is the diameter of the suction pipe known? Nu-Heat recommends 32mm (11/4″) pipe, 25mm (1″) can also be used, but the suction hose length must be reduced accordingly (see page 10 of the installation manual for details). If a smaller diameter hose has been installed this may cause suction issues.
  • How far has the underground tank been installed from the control unit? The suction hose has a maximum distance of 20m, has this been exceeded?
  • What is the height difference between the base of the rainwater tank to the base of the control in the property? Nu-Heat recommends that the height difference should not exceed 3 metres. If this has been exceeded the length of the suction hose must have been reduced to compensate for this (see page 10 of the installation manual for details). Failure to comply by these rules may cause difficulty in drawing rainwater for the underground tank.
  • How was the suction pipe run-back to the property installed? Does it lead directly from the rainwater tank to the control unit at a continuous increasing angle? Is it installed with bends and various directional changes? Any changes in direction of the suction hose will restrict the water flow and could have a detrimental effect on the performance of the pump and the system.

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