I have a Glow-Worm Ultrapower sxi. I am used to sorting out an F9 by topping up to about 1.5 bar, then the boiler fires up. However twice now I have found an F9 and after pressing the reset button the boiler fires up without any top up and the indicated pressure is >2bar. Is it possible that there is too much pressure in the system and the boiler will display F9 to indicate that as well as too little?