Booster heater does not reach sanitizing temperature; display shows E4 and machine may not allow cycle to continue.

Safety first: Shut off power to the dishmachine and booster heater at the breaker. Booster components operate at high voltage; only work on them if you are qualified.

Step-by-step checks:

• Verify incoming hot water: Measure the temperature of the water feeding the booster. If it is significantly below CMA’s specification, the booster may not be able to reach final rinse temperature.
• Reset booster high-limit: Locate the manual-reset high-limit thermostat on the booster tank. Press the reset button until it clicks. If it trips again, investigate for low water level or stuck contactor.
• Check booster elements: With power OFF and wires removed, measure resistance across each booster element. Replace any element that is open or shorted to ground.
• Inspect temperature probe/thermostat: Ensure the probe is fully inserted into the booster tank well and wiring is secure. Test with a meter for proper resistance change with temperature.
• Control and contactor: If elements and sensors are good but do not energize, the booster contactor or control relay may be faulty and should be tested and replaced by a technician.

When to call a technician: Due to high current and scalding water risk, booster heater repairs are best handled by an experienced CMA technician.