Boiler frequently loses pressure and needs to be topped up every few days, no visible leaks and no error code most of the time.

Safety: Do not continually operate the boiler with very low pressure; this can damage components.

• Check discharge pipe: Look outside at the pressure relief valve discharge pipe. If it is dripping, the valve may be passing water.
• Inspect for damp patches: Check ceilings, walls, and under floors near pipe runs for signs of hidden leaks.
• Monitor pressure: Note the pressure when cold and when hot. A large increase suggests an expansion vessel issue.
• Professional service: A technician can test and recharge or replace the expansion vessel, replace the safety valve, and pressure-test the system for hidden leaks.