Boiler displays A17, pump runs but burner does not start, especially in heating mode

Safety Warning

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

Insufficient differential pressure across Fondital boiler, Partially closed isolation valves, Blocked bypass or filter, Faulty differential pressure switch (if fitted)

How to Fix / Troubleshooting

Safety: Allow the system to cool before handling valves.

User checks:

Open valves: Confirm all heating flow and return valves under the boiler and at key radiators are fully open.
System pressure: Ensure pressure is within the recommended range.
Bleed air: Bleed radiators to remove trapped air.

Technician actions:

Check and clean the system filter and any bypass valve.
Test the differential pressure switch or flow sensor and replace if faulty.
Verify correct operation of the circulation pump and speed settings.

Repair Difficulty

Medium 3/5

Required Part

Differential Pressure Switch

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