BoilerFaultCodesTechnical description
Max.water temp.: Difference between flow and return temperature too high
What causes this fault?
This fault occurs when the boiler's internal sensors detect that heat isn't leaving the unit fast enough, causing a dangerous spike in temperature. The most common reason is a failed pump that isn't pushing water around your radiators, or a blockage caused by sludge and debris that has built up inside the pipework over time.
This issue often comes to light during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump parts to seize.
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.
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