BoilerFaultCodesWhat the manual says
Manufacturer manualFlow/Return Differential greater than 50°C
What causes this fault?
This fault occurs when the water temperature leaving the boiler is significantly higher than the water returning, usually because something is blocking the flow. The most common reasons are a failing pump that cannot push the water around your radiators or a buildup of sludge and limescale inside the pipework. When the water sits still or moves too slowly, the heat builds up too fast for the boiler to handle safely.
This issue is most common during the first cold spell of autumn, as pump rotors often seize up after being left idle throughout the summer months.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like F 0U: no call-out fees, no surprise bills.
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