BoilerFaultCodesYour boiler is currently in a manual service mode used for internal checks and is not indicating a broken part.
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: Service Mode / Sequence indicator following UF (moves diverter valve to mid-position)
What causes this fault?
This code appears when a gas engineer has manually activated the boiler's service mode to perform safety checks or internal maintenance. It physically signals that the boiler is holding its internal parts in a specific position to allow for testing, rather than responding to your thermostat. Once the engineer exits the manual sequence or the timer expires, the boiler will return to normal operation.
DIY fix possible
Turn the boiler off at the isolation switch or fused spurWait 10 secondsTurn the boiler back on to reset the control sequence
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A boiler cover plan would cover faults like DU — no call-out fees, no surprises.
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