Heatrae Sadia unvented cylinder with electronic control shows E15 and disables immersion heating.

Safety first: Isolate electrical power and allow the cylinder to cool. Do not attempt to draw off scalding water rapidly; risk of steam and burns.

Steps to address E15:

• 1. Check cylinder temperature: Carefully feel the hot outlet pipe (without touching bare metal) to gauge if the cylinder is excessively hot. If so, allow it to cool naturally.
• 2. Inspect immersion thermostat: Remove the immersion heater cover and check that the adjustable thermostat is correctly inserted into the pocket and set to the recommended temperature (typically 60°C).
• 3. Reset overheat cut-out: Many immersion thermostats have a manual reset button. Press it firmly until it clicks.
• 4. Wiring check: Ensure the immersion is wired through the thermostat and any safety cut-outs as per the wiring diagram. Do not bypass safety devices.
• 5. Replace faulty thermostat: If the thermostat does not reset or allows overheating, replace it with a genuine Heatrae Sadia immersion thermostat.
• 6. Professional PCB check: If the cylinder overheats despite a new thermostat, the PCB or contactor may be stuck on and must be checked by a qualified engineer.