Controller indicates E12; high system pressure alarm or relief valve discharge.

Safety: Hot water under pressure can cause injury. Allow system to cool where possible and wear protective equipment.

• Check pressure reading: Confirm the system pressure on the Danstoker boiler gauge. If above the design limit, isolate the automatic fill valve.
• Inspect expansion vessel: Locate the expansion vessel. Tap it lightly; if it sounds full of water, the diaphragm may have failed. Check the air charge with a gauge (system side depressurized). Recharge or replace as needed.
• Drain excess water: Carefully drain water from a drain valve until pressure returns to normal. Ensure discharge is directed to a safe drain.
• Check fill valve: Inspect the pressure reducing valve or fill valve for leakage. Replace if it continues to feed water when closed.

If E12 recurs, have a heating technician test the expansion vessel and safety devices.