Your boiler is taking a short, programmed rest to prevent itself from switching on and off too frequently, which helps protect the internal components from unnecessary wear.
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: Anti-cycle time
What causes this fault?
This occurs when your boiler reaches its target temperature and needs to pause briefly before firing up again. It is a protective measure triggered when the heat in the system hasn't dissipated yet, preventing the burner from 'short-cycling' and wasting energy. This often happens if your radiators are already hot or if the boiler's heat output is temporarily higher than what your radiators can currently handle.
This code is more common during the autumn and spring when the weather is milder and your home doesn't require the boiler to run at full power constantly.
DIY fix possible
Wait for 15 to 30 minutes as the boiler will likely restart automatically once the cooling period ends.Check that your room thermostat is turned up higher than the current room temperature.Ensure all radiator valves are fully open to allow heat to move away from the boiler more quickly.
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 3.b — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.