Help required...

Guys an Gals

I have just had a new Wylex split load CU installed by a local sparkie.
Since then, two problems have occurred that he is struggling to resolve.

The first one being;

As soon as the upstairs Ring is connected to the RCD protected side of the
CU the RCD trips.

In all fairness, he is yet to start troubleshooting this one. Thus has moved
it over to the non RCD protected side of the CU.

The other more pressing issue that needs to be resolved is this;

Whenever one of two light switches are pressed, one being a two way switch
in the hall the other being a one way switch in the kitchen, the RCD trips.
The lights are NOT on the RCD protected side of the CU. Which I believe is
normal practice. But the downstairs Ring for the sockets are... Therefore,
how would the two relate to each other unless there where to be an inter
connection between the two circuits.

So far the electrician has advised that we remove the bulbs from the two
offending lights which resolves the issue.

We are expecting a visit this coming Saturday for some extensive
troubleshooting. Therefore, if I can get some ideas in the mean time I might
be able to help him out and also reduce my bill.

I am not an electrician or even pretend to be, so if I have misinterpreted
any of the above please do not be offended.

Answers and suggestions greatly appreciated.

Cheers.