BoilerFaultCodesYour boiler is currently set to run the pump continuously, which is usually a temporary setting used during maintenance or to prevent freezing.
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: Pump mode return
What causes this fault?
This code appears when the boiler’s internal settings have been adjusted to keep the pump running all the time, rather than only when heat is needed. It is typically triggered manually by an engineer during a service or by a specific external control system that is requesting constant circulation. In some cases, a communication error between an external thermostat and the main control board can cause this setting to stay active unexpectedly.
This status is sometimes seen during extreme cold snaps if a frost protection mode has been activated to prevent the pipes from freezing.
DIY fix possible
Check if the 'Comfort' or 'Antifreeze' modes are active in your settingsTurn the boiler off and back on at the fused spur switch to reset the electronicsCheck if your external room thermostat is calling for heat continuously
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 D.18 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.