Excessive gas use

The system has presented quite a few problems since we moved into our flat in October last year.
One of the pumps has been changed as has the heat exchanger as we were gradually losing the hot water, low flow and pressure, and since then we have enjoyed 'proper' hot pressurised showers.
The latest problem was highlighted when we received our latest gas bill which was very high.
I have monitored usage against our neighbours over the last few days and we are utilising 2.5 to 3 times as much gas as them.
The boiler cycles on approximately every ten minutes for about a minute then turns off even all through the night when no water is being drawn off and the heating is turned off.
Any ideas on an answer to this problem would be appreciated.
The system has been taken out of the flat above and a conventional system installed in its place but I cannot see out landlord going along with this.
The pressure keeps dropping and the PRV has been replaced but the system requires topping up on at least a weekly basis and there is no sign of a leak.

Paradoxically, high gas consumption and the boiler constantly cycling on/off as you describe is caused by the boiler temperature control knob NOT being set to MAX. Turn it up to MAX. The boiler should then soon turn OFF and stay OFF until there is demand.

The pressure dropping IS caused by a leak. There is no other possible cause! If you have a cheapskate landlord who won't pay to get it fixed your only option is to move out and get a better landlord. I have a place available in Basingstoke if you are interested!

Cheers, Mike