BoilerFaultCodesWarmflow E04 Fault Code
The Warmflow E04 fault code means: your boiler has detected that there is not enough water pressure in the system to operate safely, which is often caused by a small leak or after bleeding your radiators.. It appears on 3 Warmflow models in our database.
Technical description: Low System Pressure — air lock, displaced NTC sensor, circulation problem, system leak, pressure loss after bleeding; check system pressure; verify corrosion inhibitor; consult if unresolved
DIY fix possible
Locate the pressure gauge on the front of the boiler or under the casing.Check if the needle is below 1 bar (usually in the red zone).Use the external filling loop to top up the water pressure until the gauge reads between 1 and 1.5 bar.
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Warmflow models that show the E04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Warmflow E04 fault code information on this page is sourced and cross-checked against the official Warmflow service / installation manuals for each affected model.
- Warmflow Agentis Boilerhouse manual (PDF)
- Warmflow Agentis External manual (PDF)
- Warmflow Agentis Internal manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026