BoilerFaultCodesRavenheat 21E Fault Code
The Ravenheat 21E fault code means: your boiler has detected that the water returning from your radiators is too hot, which has caused it to shut down for safety.. It appears on 7 Ravenheat models in our database.
Technical description: Central heating return sensor overheating
What causes the Ravenheat 21E fault?
This fault occurs when the water traveling back into the boiler from your radiators becomes excessively hot, causing the system to shut down to prevent internal damage. The most common reason is a lack of water circulation, often caused by a failing pump or a buildup of sludge and debris that blocks the main heat exchanger.
This fault is more common when the heating is first turned on after summer, as circulation pumps can seize up during long periods of inactivity.
DIY fix possible
Ensure all radiator valves (TRVs) are fully open and not stuck.Check that the internal boiler pressure is between 1 and 1.5 bar.Reset the boiler using the control knob or button to see if the fault clears.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ravenheat models that show the 21E fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ravenheat 21E 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