The answer to 'water heater not cooling' is that the issue is likely due to a faulty thermostat or a problem with the heating element. The thermostat may be set too low, or it could be malfunctioning and not triggering the heating element properly. If the heating element is worn out or damaged, it will not be able to effectively heat the water in the tank.
Some common symptoms of a water heater not cooling properly include lukewarm or cold water coming from the taps, the tank taking longer to heat up, or the water not getting as hot as it should. To troubleshoot the issue, you can first check the thermostat setting and adjust it if needed. If the problem persists, you may need to replace the thermostat or the heating element, which is a more involved repair that is best handled by a professional HVAC technician.