Confirm whether your Miele machine is plumbed to both a hot and cold water supply. On dual-supply models there are two hoses at the back of the machine — a cold inlet (blue or unmarked) and a hot inlet (red or marked H). If your machine has only one hose it uses a cold supply only — in this case F15 may indicate a thermistor or valve conflict and you should proceed to the diagnostic steps below.

Find the hot water isolation tap on the hot water supply pipe and turn it fully anti-clockwise. If the hot supply tap has never been used it may be stiff — turn it carefully without forcing it.

Turn the hot tap off. Disconnect the hot inlet hose from the machine. Inside the hot inlet port on the machine body is a small mesh filter — often more heavily scaled than the cold inlet filter because hot water deposits limescale more aggressively. Remove with tweezers, soak in white vinegar for 5 minutes, then scrub with a toothbrush and rinse. Refit firmly.

Disconnect the hot inlet hose and briefly open the hot tap into a bucket for 3 seconds. You should see a strong, steady flow of hot water. If the flow is significantly weaker than the cold supply, the hot water system pressure is low — contact your plumber.

With the machine completely unplugged and water off, remove the rear panel. The hot inlet valve is the additional solenoid valve connected to the red or hot inlet hose. Test the coil resistance with a multimeter — a healthy solenoid typically reads between 200 and 1,500 ohms. An OL (open circuit) reading means the coil has failed.

Reassemble everything, turn both hot and cold supplies fully on and run a 60-degree Cotton programme. The machine should fill normally from both inlets without displaying F15.