Combi boiler Baxi 105e instant?

Hi,
I have a 2 year old Baxi 105e instant combi boiler, recently within the last month I have noticed the boiler losing too much pressure [I have replaced the pressure valve but this has not solved the problem] The pressure guage on the front panel keeps dropping to the zero mark I am constantly charging the system with more water. Also I have noticed too much water draining through the external overflo pipe. Can anyone please help?
Wishing you a Happy & Prosperous New Year
Adam