Grant Heat Pump: DHW Priority Preventing Heating - UK Fix
Fix Grant UK heat pump issue where domestic hot water priority prevents heating from working. Expert diagnostics and solutions. Boiler Upgrade Scheme (BUS) tips.
Fix Grant UK heat pump issue where domestic hot water priority prevents heating from working. Expert diagnostics and solutions. Boiler Upgrade Scheme (BUS) tips.
© 2026 heatpumpfaults.co.uk
Generally, 60°C is a good balance between hot water availability and energy efficiency. Check the Grant installation manual for specific recommendations.
Use a radiator key to open the bleed valve at the top of each radiator. Allow air to escape until water starts to flow. Be prepared with a cloth to catch any drips.
The pre-charge pressure should be set according to the system's static head height, typically around 0.5-1.0 bar. Consult the heat pump installation manual or a qualified engineer for specific guidance.
Access the Grant heat pump installer menu to view real-time sensor data and error logs. This can help pinpoint the source of the DHW priority issue. Check the flow rate to the cylinder during DHW demand; it should be within the manufacturer's specifications.
When domestic hot water (DHW) is demanded, the heating circuit shuts down completely. No flow to radiators is detected, even with thermostats calling for heat. Audible change in compressor frequency during DHW demand. App-side telemetry shows heating circuit at 0W power consumption during DHW cycle. Reduced radiator temperature and increased DHW cylinder temperature noted.
Grant heat pumps utilise a priority system to ensure sufficient hot water is available. This involves diverting the entire heat output to the hot water cylinder until the setpoint is reached. The refrigerant cycle is optimised for DHW production during this phase, increasing the hot gas temperature at the expense of flow to the heating circuit. Weather compensation is temporarily overridden. Cylinder temperature sensor calibration impacts this logic. System relies on correct flow rates and pressure differentials.
Implement an annual MCS service. Check system pressure and expansion vessel pre-charge. Regularly bleed radiators. Monitor DHW cylinder temperature and adjust setpoints as needed. Inspect for leaks and corrosion. Ensure inhibitor levels are maintained in the system water. Schedule a G3 safety check.