Error 503 while accessing domain

Hey, I have ordered domain and VPS recently, deployed my page and tested it.

All works fine apart from accessing the site for users based in UK - sometimes when I want to access it I receive error 503:
"Error 503: Unknown domain
This type of error results generally from a domain not totally installed."

This only happens to users accessing site from UK. I tested it from USA and Poland and this error is not shown there. It looks like a problem with one of load balancers not having information about my domain but perhaps something's wrong with configuration of domain. What I have done is just added new entry in DNS zone with my server IP and that's it. Perhaps something else is needed there?