Grant Insufficient Domestic Hot Water Temperature

Boiler runs but domestic hot water from taps is lukewarm or runs hot then quickly cold.

Advertisements

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Advertisements

Possible Causes

Cylinder thermostat set too low or faulty, Plate heat exchanger partially blocked (combi/heat-only with plate), 3-port valve not fully diverting to DHW, Scale build-up in cylinder coil

How to Fix / Troubleshooting

Safety: Beware of scalding when testing hot water. Cylinder temperatures should be at least 60°C to prevent Legionella.

User checks:

  • Check the cylinder thermostat setting (typically 60°C) and increase if set too low.
  • Ensure the programmer is set to provide hot water at the desired times.

Engineer actions:

  • Test the cylinder thermostat for correct switching and replace if faulty.
  • Inspect the 3-port or DHW zone valve for full travel to the hot water position.
  • Check and clean the plate heat exchanger if fitted and partially blocked.
  • Assess the cylinder coil for scale; powerflush or replace cylinder if severely affected.
Advertisements

Repair Difficulty

Medium 3/5

Required Part

Cylinder thermostat
Check Price on Amazon

We may earn a commission from links on this page.

Advertisements