Budurus GB142 Question

I've done a few searches but can't seem to find out if this boiler uses any water during normal operation?

The reason I ask is we've been getting the H7 low pressure error and have to lift the lever on the feed valve (Watts 1156F) to bring the pressure back up, so that's due for a cleaning or replacement. System loses about 2 psi over a 2-3 week period. Since water is only being fed in manually now, I'm wondering if the use is normal or if it may be an indication of a slow leak somewhere?

Thanks for any input.