A12
De Dietrich
Flow Switch / Minimum Flow Fault (Heating Circuit)
Boiler shows A12, no heating, pump may run briefly then stop
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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.
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Possible Causes
Closed radiator valves, blocked system filter, stuck differential pressure switch, air in system
How to Fix / Troubleshooting
Safety: Allow the system to cool before bleeding radiators or opening filters. Protect floors from water spills.
- Open valves: Ensure all radiator and underfloor manifold valves are open to allow sufficient flow.
- Bleed air: Bleed radiators and any automatic air vents near the boiler. Re-pressurise the system afterwards.
- Clean system filter: If a magnetic or dirt filter is installed on the return, isolate and clean it thoroughly.
- Technician tasks: A heating engineer should check the boiler's internal flow switch or differential pressure sensor and replace if stuck or faulty.
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Repair Difficulty
Medium
3/5
Required Part
Heating Flow Switch / Differential Pressure Sensor
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