Your boiler is taking a short, programmed break to prevent itself from turning on and off too frequently, which protects the internal components from unnecessary wear.

What causes this fault?

This occurs when your boiler reaches its target temperature too quickly and needs to pause to prevent 'short-cycling,' which is like a car stalling in stop-start traffic. It usually happens because the heat produced by the boiler cannot be moved away fast enough, often because your radiators are already warm or some have been turned off. The boiler is simply waiting for the water in the system to cool down slightly before firing up again to work more efficiently.