BoilerFaultCodesWhat the manual says
Manufacturer manualMaximum set value for target cylinder
Shared across the range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
DIY fix possible
Check the hot water temperature settings on your control panel to ensure they aren't set too highMonitor the boiler to see if the central heating and hot water continue to operate normally once the temperature dropsIf the code persists, try resetting the boiler once
Find a Gas Safe engineer
Search the official register →
Boiler cover options
Avoid the next call-out bill
A cover plan would handle faults like D.20: no call-out fees, no surprise bills.
Approved partner
Get a quote →
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Affiliate links. We may earn a commission at no extra cost to you.