ferroli f 28 losing pressure?

hi, my boiler is losing water at an alarming rate...i've checked all under floor pipework, nothing, bone dry. no water around the boiler at all.

i shut off the feed and return valves to the radiators, turned the boiler off completely, topped the boiler up to just above 1 bar, i then disconnected the condensate pipe and sat it in a bucket. i left it like that overnight, in the morning the boiler pressure was at zero, and the bucket was one third full of water, is this a secondary heat exchanger issue or can anyone advise.

i called british gas to get their one off repair deal, the guy came out and said he can't touch my boiler as it's not on their service list.

my boiler is a 3 year old ferroli domicondens f 28