Sounds like there is air trapped in your system caused by the meter change-over. Is there any way of contacting the water company to complain that their engineer has caused this fault and see if they can offer a way of rectifying this 'damage' they've caused? Just a thought...
If it is an airlock issue, I've found a link that may help you if you have the skills to carry out the necessary works required to vent the system yourself:
https://www.diydoctor.org.uk/forums/system-venting-t9456.html
Rupert, February 2020
