D.20 Low
Your boiler is notifying you that it has reached the maximum temperature allowed for your hot water cylinder.
Technical description: Maximum set value for target cylinder
Typical repair cost: £0-60 (including labour)
DIY fix possible
Check the hot water temperature settings on your boiler control panelReduce the target cylinder temperature if it is set too highMonitor the boiler to see if the code clears once the water temperature stabilizes
Protect yourself from future repair bills
A boiler cover plan would cover faults like D.20 — no call-out fees, no surprises.
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Parts commonly replaced
- None (parameter adjustment)
- Cylinder NTC thermistor
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