A possible problem with a yellow LED and no small bubbles is due to a (too) late descaling.

Our advice is to check the electrolysis unit for limescale at least every 2 to 3 weeks (in the beginning, 1 x a week, preferably at a fixed time to get to know the system). In areas with hard to very hard water, such as Southern Europe, it may even be necessary to check for limescale every 3 to 4 days!
If necessary, clean/descale with cleaning vinegar or citric acid.

By descaling the cell core at regular intervals, adapted to the lime content in the water, you avoid damaging the electrolysis unit. With regular checks, decalcification takes only about 30 minutes and ensures an optimal lifespan of the cell nucleus. TIP: If you are absent for a few hours to do some shopping or something else,
put the Tank-O3 fresh water system firmly in a bottle of cleaning vingar, the system will be 100% clean again when you return. Make a habit of doing this every 4 to 5 days and you will prevent the limescale problem!

Note: If you fail to descale the electrolysis unit in time, the limescale can accumulate under the cell core. The accumulated limescale hardens and then presses the clamps that hold the cell nucleus to pieces, or worse: the tip at the top of the electrolysis unit breaks off, resulting in the necessary repair* or replacement of the most expensive part, the electrolysis unit! This is visible in the bottom photo. Despite the placement of a new cell nucleus, the yellow LED will continue to burn.
The risk is therefore minimized by regular checks. This prevents a repair* or costly replacement of the entire electrolysis unit with cell nucleus.
Prevention is better than replacement!

* Repair means that you send the electrolysis unit to us, preferably in a letterbox package with Track & Trace number! We then replace the pin and install a new cell core. The repair costs are € 10,00 + a new cell core at € 39,95 + € 15,00 shipping costs (€ 10,00 in the Netherlands), so a total of € 64,95. Our address details:
Tank-O3 fresh water system, Albardastraat 61, 5344 HB Oss (NL). info@tank-o3.nl +31625119528