BoilerFaultCodesRavenheat E21 Fault Code
The Ravenheat E21 fault code means: your boiler has detected that the water returning from your radiators is too hot, causing the system to shut down to prevent damage.. It appears on 9 Ravenheat models in our database.
Technical description: Central heating (CH) return sensor overheating
What causes the Ravenheat E21 fault?
This fault occurs when the internal sensors detect that the water flowing back from your radiators is at a dangerously high temperature, suggesting the heat isn't being dissipated correctly. The most common reasons are a blockage in the system, a failing pump that isn't circulating water fast enough, or a faulty sensor sending incorrect readings to the boiler.
This issue often comes to light during the first cold spell of autumn when the heating is turned on for the first time after summer, often due to a pump that has seized while sitting idle.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barSwitch the boiler off and on again to see if the fault clears after the system cools down
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Gas Safe Register →Ravenheat models that show the E21 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ravenheat E21 fault code information on this page is sourced and cross-checked against the official Ravenheat service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026