Falling Boiler Pressure

I have been experiencing falling pressure with a Sealed System Boiler
set up. I have my central heating zoned. I have no pressure loss when heating upstairs only- but lose pressure when heating the ground floor only. I have added Firnox leak repair and this has had some effect- slowing down the pressure loss significantly. However if there is a leak to the pipework on the ground floor I am faced with rolling back carpet and lifting floorboards to trace the piepwork and try to spot the leak.
Or is there another way to do this? Is there a damp meter or water diving
type of instrument that would help me spot a leak underneath my floorboards- so that I can pinpoint the problem staightaway?

If you have a leak under the floorboards you will still have to get them up to repair.

You have to bite the bullet and scour everyinch of your pipework to find it.
Rad bleed points and feeds and PRV should be your first port of call.

Most popular place for a leak is one of the valves on the rads.
Sometimes it's not obvious because the hot pipes dry off the evidence, although there's often a stain. Checking when it's cold might show it, but sometimes the only leak when hot.
Other than that, it's up with the floorboards, I think.