The heating and hot water red lights were flashing slowly and boiler wouldn't ignite to provide hot water. Previously repressurising the system cured this so attempted again. This time when the pressure of 1bar was reached, turning on the system extinguished the lights but when hot tap turned on the gas burner ignited only for approx 10 seconds, banging noises within the system, followed by steam/hot water/air venting from the air vent on top of boiler. Used pressure relief valve to release pressure in system but the above still occurred when turned on again. Any help please????