Heater will not turn on, display shows E04 or heater icon flashes and then shuts off.

Safety: Disconnect power and allow the heater and solution lines to cool completely before servicing. Risk of burns and electric shock.

• Reset high-limit thermostat: Locate the solution heater assembly (often a stainless steel tube or block). Find the manual-reset high-limit thermostat (small button on a disc). Press the reset button firmly until it clicks. Restore power and test. If it trips again quickly, investigate flow restrictions or thermostat failure.
• Check solution flow: Low or no flow through the heater can cause overheating. Inspect inlet strainers, inline solution filters, and jets for blockages. Clean or replace filters and flush lines.
• Test heater element: With wires removed, measure resistance across the heater terminals. An open circuit indicates a failed element. Replace the Prochem solution heater assembly or element as supplied by the manufacturer.
• Inspect temperature sensor: Many Prochem units use an NTC sensor on the heater. Check the sensor connector and wiring. Measure resistance and compare to service data (typically a few kΩ at room temperature). Replace the solution temperature sensor if open or shorted.
• Heater relay / PCB: If the heater and sensor test good but no voltage is supplied to the heater when commanded, the heater relay on the control PCB may be defective. Replace the control PCB or have the relay professionally replaced.