Gas boiler - water pressure

Hi since getting my gas boiler serviced 2 weeks ago, water has been coming out of the water outlet at the side of the house. I've been told by a local builder that it's due to water pressure being too high & I should get Bord Gais out as they serviced it.
I took out boiler insurance so I'm just wondering if this is a small thing & if it would be covered?

Problem could be
1/ the filling loop could still be open allowing more water into the system.
2/ expansion vessel could be faulty. Red cylinder at back of boiler
3/ they might have opened the pressure release valve which might not have closed properly.

Call them back as it shouldn't be a major problem.