Unable to locate the leak

First port of call check under bath by removing bath panel, use your fingers to check the pipes leading to the taps first, then check around the bath waste. Also check the bath sealant (mastic) to make sure its water tight when using the bath or shower if you have bath mixer. If this is all dry, id say you have a leak on an heating pipe which would also explain the pressure loss a the boiler. Leaks can be easy or an absolute nightmare to locate, it really is a case of elimination. A good plumber will be able to assist and repair. Good luck

no not realy you will have to take bath panel off and check under bath if it is not there you will have to start lifting floor in bathroom.it could be a leak in central heating do you have a towel rail or rad in bathroom check valves first if not leaking you will have to take up floor to check pipes.

Hi Is the ceiling underneath the bathroom wet or dry? If dry, it might have been a one off spillage. If wet, check all the pipes/taps/drains connections in the bathroom first. What’s the floor type in the bathroom?

First port of call would be the loss of pressure in the heating system, if the leak persists after that its purely a matter of investigation and elimination

Before you do any of the above, is the sealant around the edge of the bath intact, as this tends to be a common cause of damage beneath a bathroom, you can check the bath is sealed by removing the bath panel then spraying the shower round the edge of the bath from above then check for water coming down the back edges of the bath. This may not be the problem, just an idea before you pull any flooring up.

If you try all of the above and no result, then buy/hire a thermal imaging camera and check for the leak with central heating on first then hot water