BoilerFaultCodesYour boiler is currently set to run at its maximum possible heating temperature, meaning it is working as hard as it can to heat your radiators.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Maximum setting of heater control knob
What causes this fault?
This code appears when the heating temperature dial or digital control has been turned up to its highest possible setting. It occurs because the boiler is being instructed to deliver its maximum heat output to the radiators, often after someone has manually adjusted the controls for more warmth. It is a status indicator rather than a broken part.
This is more common during extreme cold snaps in winter when homeowners turn their thermostat or boiler dial to the maximum setting to combat the freezing weather.
DIY fix possible
Locate the heating control knob on the front of the boiler panel (marked with a radiator icon).Turn the knob slightly to the left to reduce the target temperature to a more efficient level (e.g., 65-70°C).Observe the display to ensure the temperature setting has updated.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like D.71 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.