BoilerFaultCodesWhat the manual says
Manufacturer manualHigh Flow/Return Differential, 3 times in succession and Flow Temperature <7°C
What causes this fault?
This fault occurs when the boiler detects that water is not moving through the system quickly enough to carry heat away, combined with an internal temperature that is dangerously close to freezing. The most common reason is a blockage in the pipework or a failing pump that prevents the water from circulating. Because the water is sitting still in freezing conditions, the boiler shuts down to prevent the internal pipes from cracking due to ice expansion.
This fault is almost exclusively seen during the winter months, as it requires both a circulation issue and an external temperature low enough to drop the unit's internal water below 7°C.
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 Hb: no call-out fees, no surprise bills.
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