BoilerFaultCodesYour solar hot water system hasn't reached the high temperature needed to kill bacteria, usually because the solar pump is struggling or the settings are incorrect.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Temperature for thermal disinfection not reached in solar cylinder. Maximum temperature for solar cylinder too low / Delivery rate of disinfection pump (PE) too low.
What causes this fault?
This fault occurs when the water in your solar cylinder fails to reach a high enough temperature to safely eliminate bacteria like Legionella. The root cause is typically a circulation issue where the solar pump isn't moving enough fluid, or the system settings are preventing the tank from getting hot enough to complete its weekly disinfection cycle.
This fault is more common during the winter months when there is insufficient solar gain to naturally heat the cylinder, placing more reliance on the pump and auxiliary settings to reach the target temperature.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like Fault 54 145 — no call-out fees, no surprises.
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