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Heater indicator light is off and not heating water

This is one of the most common "problems" that is often easy to fix. We'll first explain the construction of the heater and how the various components work together.

The heater has a flow guard (FS) that moves from the water flow provided by the circulation pump. The flow through the heater needs to be at least 3600 l/h for the flow switch to activate the microswitch (MS). It then supplies current to the heating element until the set water temperature has been reached. During the time that it is heating, the indicator light (ML) also lights up.

If the water flow is insufficient, there will not be enough water flow to move the paddle enough to activate the microswitch (MS). If there is too little water, the pump starts to suck in air and then the overheating protection (T2) can trip. The cause can also be a dirty filter.

If any of the above occurs, the circuit is broken and the heating element cannot function.

Watch the video carefully and it will be easier to understand the text. Also feel free to pause the video to be able to read the text and look at the picture at the same time.

Faults that may occur to cause the heater not working:

  1. The most common reason for the heater not working is dirty filter media. This means that the water flow is not sufficient for the flow monitor (FS) to activate the microswitch (MS) and then current does not pass on to the heating element. The lamp on the heater then does not light up either.
    Corrective action: Remove the filter cartridge and try without. If that works, the cause of the problem has been located and the solution is to change to a clean filter. Be sure to follow instructions on how to clean filters.

  2. If the temperature inside the heater for any reason exceeds 60 °C, e.g. if the pump sucks air, the overheating protection (T2) trips and the circuit to the heating element is broken. ATTENTION! A clear sign that the pump is taking in air is if you can see air bubbles coming up from the bottom or you hear a "slurping" sound or "uneven" movement from the pump.
    Corrective action: Check that the water level is sufficient. If that was not the cause of air, check that the connections are tight around the air screw and cover for the filter, otherwise the pump can suck in air when it is running. Turn off the pump, if water comes out around the filter it needs to be fixed. A dirty filter can also lead to the formation of air in the water flow and is checked as described under point 1. If overheating is resolved, a reset must be done. Unscrew the black round protection to (T2) and push in the "reset pin".

  3. A thermostat error also means that current does not pass to the heating element.
    Corrective action: Try setting the thermostat knob between minimum and maximum. If a faint click is then heard, the thermostat is OK. If no click is heard, the thermostat may be broken and needs to be replaced. If you have a digital thermostat, it can replace the heater's own thermostat, which can then be bypassed.

  4. Micro switch (MS) rarely causes errors but if it does, current does not pass to the heater.
    Corrective action: On the microswitch there is a small "knob" and when it is pushed in, a click should be heard, in which case it is complete. IF it is not heard, the microswitch must be replaced.

>> Figuring out the reason why the heating does not work can also be done by measuring the current circuit.

Electric scheme SDH.jpg

Digital thermostat settings and thermostat errors can also cause the heater to not function.

  • If there is a digital thermostat and the temperature falls below the set temperature, the temperature sensor should detect this and a small red dot should then light up in the upper left corner of the digital thermostat's display as a sign that it is giving out power to the heater.

  • If the dot is not visible, the settings in the digital thermostat must be checked. Make sure parameter HC is set to H and go through the others and make sure they follow what is described in the instructions. See also this video! If it still doesn't work (small red dot in the top left corner doesn't light up), then the thermostat may be faulty, although this is unusual.

    According to the instructions, the knob on the mechanical thermostat must always be set to the maximum position if a digital thermostat is used. The function can be checked by turning the thermostat knob between minimum and maximum. If a faint click is then heard, the thermostat is OK. If no click is heard, the thermostat may be out of order and needs to be replaced. BUT, if there is also a digital thermostat, the heater's (RS1) own thermostat is not needed and it can be bypassed.

Here are also various instructions that come with the products:

Excl. VAT62.50
Inc. VAT77.50
Excl. VAT62.50
Inc. VAT77.50
Excl. VAT176.00
Inc. VAT218.24
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