E4 appears shortly after starting a pressure program; cooker stops and may beep continuously.

Safety first: Unplug the unit and allow pressure to drop naturally. Never force open the lid while under pressure.

Correct usage checks:

• Verify liquid level: Ensure you are using at least the minimum liquid specified in the MasterPro manual (often 250–500 ml). Very thick sauces or high-starch foods can trigger dry-boil protection.
• Clean steam paths: Remove and clean the steam release valve, anti-block shield, and inner lid. Food buildup can restrict steam flow and cause overheating at the base.
• Inspect inner pot: Check for severe scratching or flaking of the non-stick coating. Damaged coating can cause sticking and localized burning.

Component checks (unplugged):

• Remove the bottom cover to access the thermal fuse and bimetal thermostat mounted on or near the heating plate. Check for signs of overheating or discoloration.
• If the thermal fuse is open (no continuity), it must be replaced with the same rating. A repeatedly tripping thermostat may also need replacement.

Note: If E4 occurs even with correct liquid levels and clean components, the control board may be misreading temperature and should be evaluated by a technician.