BoilerFaultCodesYour boiler's internal temperature sensors have likely been crossed or wired incorrectly, meaning the system cannot safely monitor how water is circulating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The heating flow thermistor and heating return thermistor are connected the wrong way round.
What causes this fault?
This fault occurs when the boiler's internal computer detects that the temperature readings for water leaving the unit and water returning to it are reversed. The most common reason is that the physical sensors have been swapped during a recent repair or the wiring harness has been plugged into the control board incorrectly. Because the boiler cannot accurately track how heat is moving through the system, it shuts down as a safety precaution to prevent overheating.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like 00 — no call-out fees, no surprises.
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