This video shows how to test that electronics are working. The On/Off button must be in the On position. With a narrow flat screwdriver, the microswitch is activated (the red lamp lights up) as shown in the picture. The same happens when the heater gets enough water flow.
If it does not light up, despite the batteries being in place with the correct polarity (yellow wire at the top) and the microswitch has been activated, then check that there is no loose contact in the yellow/red wire connections.
Normal mode and ignition when the pump starts. Note that the sheet on the microswitch moves. This assumes that the pump provides sufficient water flow. If, for example, the filter is not clean, it reduces the water flow. So be careful to check and if necessary clean it.
Testing igniter and burner
Here it is shown how the left and right igniter (flame protection removed) gives a spark immediately at start-up. Igniters need to be cleaned at least once a year. This can be done by scraping/polishing the outermost tip.
Ignition fuse for the gas burner
The ignition fuse that can be seen in the middle has the task of ensuring that the gas that flows out of the burner also burns. If there is not enough fire, or not at all, the gas supply is shut off. In the video here; https://youtu.be/10EL-svuG7I it burns weakly where the ignition fuse is and this causes the gas supply to be shut off and everything goes out. In this case, the burner and in some cases nozzles must be cleaned.
This is most easily done by using compressed air and blowing into the burner above where the flame burns weakly or not at all. A compressed air can also be used. First remove the flame guard in front of the burner by removing the screws on the left and right. Also blow on the brass nozzles directly below where the burner is to be cleaned.