D.75 High
Your boiler has timed out because it has been trying to heat your hot water cylinder for too long without reaching the required temperature.
Technical description: Maximum charging time for a storage without own controller
Typical repair cost: £100-280 (including labour)
DIY fix possible
Check that the valves on your hot water cylinder are fully openEnsure your thermostat or programmer is calling for hot water correctlyTry resetting the boiler to see if the fault clears
Protect yourself from future repair bills
A boiler cover plan would cover faults like D.75 — no call-out fees, no surprises.
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Parts commonly replaced
- NTC Temperature Sensor
- 3-Port Diverter Valve
- Cylinder Thermostat
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