Lowering presser everyday in Baxi105 instant HE?

I got 3Years old boiler.works ok,but water presser goes down everyday.I have to fill water in boiler everyday.
May be leak in system. Drain valve checked.I can not find leak in boiler.Leak in boiler some where.Found water under boiler.

Can you advice me,what to check ?

Is common foult in Baxi 105 instant HE Boiler.