Electric water heater getting too hot

the small deposits would be limscale. try buying an ionic shower head from amazon, they have small filters that help to minimise scale

1. **Shower Head Compatibility**: Ensure that the shower head is the manufacturer's original part or a compatible replacement. Using an incorrect shower head can lead to pressure issues within the unit, which might be causing the overheating. 2. **Internal Deposits**: If your unit is quite old, the deposits might be from the internal components, such as the heater element. Over time, mineral buildup can occur, especially in areas with hard water. This can reduce the efficiency of the heater and cause overheating. In such cases, a replacement might be the only effective solution, as attempting repairs on an old unit could be as costly as a new one. 3. **Water Hardness and Filtration**: While you've ruled out limescale, it's worth reconsidering the possibility of mineral deposits from hard water. An ionic shower head, could help minimize scale buildup. Additionally, consider installing a whole-house water softener or a point-of-use filter for the shower to reduce mineral content in the water. 4. **Regular Maintenance**: Regular maintenance and descaling can prolong the life of the heater and prevent issues. If you haven't done so already, consider scheduling a professional inspection and maintenance service. 5. **Safety Measures**: Since overheating can be a safety hazard, it's crucial to address this issue promptly. Ensure that the temperature settings on your unit are correct and consider installing a thermostatic mixing valve, which can help regulate water temperature and prevent scalding. 6. **Consult a Professional**: Given the recurring nature of the problem and the potential complexities involved, it's advisable to consult a certified plumber or an electrician specializing in water heaters. They can provide a detailed diagnosis and recommend the best course of action, whether it's repair, part replacement, or a new unit installation. In summary, while replacing the unit might ultimately be necessary, especially if it's old, exploring these options can help you identify and address the root cause of the overheating issue.

Have you ever replaced the head on the shower? Electric showers should always be replaced by the manufacturers original part, the wrong head can cause a pressure problem in the shower unit causing it to fail over a period of time. If the shower is quite old, say 10-15 years those deposits could be a build up inside the heater element itself, there's no real solution to that other than a replacement unit. Don't bother trying to get it repaired, it will cost as much as replacing, and if it's that old other parts will be wearing out also.