BoilerFaultCodesYour boiler has detected that hot water is not moving around the system properly, causing it to shut down to prevent overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Primary water circulation fault
What causes this fault?
This fault occurs when water is unable to flow through the boiler quickly enough, leading to a sudden rise in temperature. The most common reason is a failed internal pump or a blockage in the system caused by a buildup of sludge and debris. It can also happen if there is an air lock or if the radiator valves are all turned off, preventing the heat from escaping.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle all summer, which can cause internal pump parts to seize.
DIY fix possible
Check that the boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeEnsure all radiator valves are fully openCheck if any air is trapped in your radiators and bleed them if necessaryRestart the boiler by turning the selector switch to the 'R' position for five seconds
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 E125 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.