Boiler shows A16, display may flicker or reboot, random lockouts

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Unstable mains voltage, Loose mains terminal connections, Faulty internal power supply on PCB, Shared circuit with heavy loads causing dips

Safety: Isolate power before tightening terminals. Electrical work should be done by a qualified electrician or heating engineer.

Steps:

Check that the boiler is connected to a dedicated fused spur with correct fuse rating.
Inspect the mains terminal block inside the boiler for loose screws or signs of overheating; tighten as needed.
Measure mains voltage under load; if outside IVT limits, consult an electrician.
If supply is stable but A16 persists, replace the main control PCB after verifying all external wiring.

Hard 4/5

Main Control PCB

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