Boiler shows A16, frequent short cycling, limited modulation

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

Defective Herz modulating gas valve, faulty modulation signal from PCB, damaged wiring harness to gas valve, incorrect gas type configuration

Safety: Gas components must only be adjusted or replaced by licensed gas technicians.

Visual inspection: Check the gas valve connector and cable for damage or loose pins.
Confirm gas type: Ensure the boiler is configured for the correct gas (natural gas or LPG) as per Herz data plate.
Do not adjust screws: Do not attempt to adjust gas valve screws without a combustion analyser and Herz procedures.
Call technician: A Herz-certified technician should test the modulation signal and replace or calibrate the gas valve if necessary.

Professional Required 5/5

Herz modulating gas valve

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