BoilerFaultCodesGrant DHW PUMP Slow flash Fault Code
Also written as DHWPUMPSLOWFLASH — same fault.
The Grant DHW PUMP Slow flash fault code means: your boiler's control computer is failing to communicate correctly with the water heating pump, which means the system cannot reliably produce hot water.. It appears on 3 Grant models in our database.
Technical description: Indicates a possible fault with the PCB (relay). Replace PCB.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Grant models that show the DHW PUMP Slow flash fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Grant DHW PUMP Slow flash fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.
- Grant Vortex 15-20 manual (PDF)
- Grant Vortex Eco manual (PDF)
- Grant Vortex Eco External Wall Hung manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026