I had exactly this happen today. I stupidly left the valves closed to a magnetic in-line filter, having cleaned it, and started the boiler. It ran for two minutes and then closed down. Fault F5 left me perplexed but luckily our plumber realised you need only to press the reset button that is located on the upper left corner between two copper feed pipes. It is triggered by overheating, and simply needs to be pushed in to re-close the circuit.
PaulT, January 2017
