BoilerFaultCodesYour boiler has detected that the water coming back from your radiators is hotter than the water leaving the boiler, which usually means water is flowing in the wrong direction or a sensor has developed a fault.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature measured by return sensor greater than flow sensor.
What causes this fault?
This fault occurs when the boiler detects that the water returning from your radiators is hotter than the water it just sent out, which contradicts the laws of physics in a normal system. The most common reasons are a pump that has failed or is struggling to push water around, a blockage in the heat exchanger, or temperature sensors that have become uncalibrated and are giving false readings.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as internal pump components can seize during long periods of inactivity.
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 E.01 – .02 — 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.