Baxi boiler losing pressure, been topped up on loop but still dropping.?

just to add to what others have said check your condenste line for water when not running, you could have a leak in the heat exchanger

Either there is a leak or the safety valve is letting by. Have a look outside at the copper pipe with a couple of short bends in it. If this is dripping that's the cause. You should be able to briefly turn the safety valve on and off which may clear any debris. See your installation manual for details. If it still drips a new one is required. The other option is a leak somewhere in the heating pipework. Check around rad valve joints and look for water stains on ceiling etc. This is best done when the heating is off as small leaks evaporate off quickly from hot pipes.

if you cant see the leak then its on the ground floor ..check both rad valves on every rad ..but most pipework is under floor

You have a leak somewhere in the system. Or you have air in the system. The leak might not be obvious.

Check for a leak.