Your boiler has lost contact with its outside weather sensor, so it is heating your home as if it were freezing outside, which may make it run warmer or longer than necessary but it should still provide heating and hot water.

DIY fix possible

Check that the boiler's wireless base station (the small box connected to the boiler) has power and that its indicator light is on.Check the batteries in the wireless outside temperature sensor and replace them if they are low, following the manufacturer's instructions.Make sure the outside sensor is mounted on a shaded north or north-facing wall, away from windows, vents and direct sunlight, and that nothing is blocking the signal path between the sensor and the base station.Switch the boiler off at the control panel for a few minutes, then switch it back on so it re-establishes communication with the sensor.If the code returns, contact a Gas Safe registered engineer to test the wireless signal and replace the sensor or base station if needed.