Yes you may well have a point. It's enough leakage to buckle plastic floor tiles, but that could have been over several months. Thanks for your response.
We have 35 year old copper microbore underfloor that now leaks on one run, minutely, but enough to have to correct. However there is no pressure drop whatever showing on our Vaillant boiler. According to all the forums I've ever read this is impossible. Comments eagerly awaited.