BoilerFaultCodesYour boiler is having trouble communicating with the pump that fills your external hot water tank, meaning your hot water supply may be affected.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Function relay 2: External cylinder loading pump
What causes this fault?
This fault occurs when the boiler's control system loses its electrical connection to the pump responsible for heating your hot water tank. The most common reasons are a loose or damaged connection in the internal wiring harness, a failure of the relay module that sends power to the pump, or the pump's motor itself drawing too much current and causing a communication error.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like 53:3 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.