Combi boiler Baxi 100HE
I have 2 small leaks at radiator valves, about half a cup a month. I am
not plumbing experienced so wont tackle the leaks until the heating goes
off in Summer (just in case) so every couple of months I need to top up
the pressure. I mention this in case it is relevent.

Today I noticed the external vent had some water come out of it, from
what I can gather it was around the time the heating came on at 5pm, I
checked later and it appears to have dried up, so maybe a one off.

It is unlikely that I over pressured the system as I have done this many
a time and pressure to 1.5 bar.

I will check again tomorrow to see if it vents if so what should I next
check. If not why a one off as never noticed this before in the 2 years
been in the house.