Boiler displays error code 30, pressure rises rapidly when heating, then discharges via safety valve

Warning: Hot water may discharge from the safety pipe. Keep clear of the discharge outlet. Do not cap or block the safety pipe.

• Check cold pressure: When the system is cold, ensure pressure is around 1.0–1.5 bar. If higher, carefully drain some water from a radiator drain point to reduce pressure.
• Observe pressure rise: Turn on heating and watch the gauge. If it climbs above 3 bar and water discharges outside, the expansion vessel is likely not functioning.
• Do not keep topping up: Repeatedly adding water will worsen corrosion and does not fix the underlying issue.
• Engineer tasks: The engineer will check and recharge or replace the expansion vessel, verify the connection pipe is clear, and test/replace the pressure relief valve if it has been damaged by repeated discharge.