City water gauge moves slightly. Is this indicative of a radiant in floor leak?

One month ago I purchased a patio home with hydronic in floor heat. Recently as the electric mini boiler was running and feeding newly heated water through the pipes I noticed that the tiny triangle of my city water gauge was moving ever so slightly. (No other water was being used during this time). Is this indicative of a leak in the piping somewhere or is a miniscule use of water normal? If this is indicative of a leak what should I do next?