I found that part of code when I searched 'runtime error 5631' and found it in another forum somewhere.

This is the error here:

Run time error 5631
Word could not merge the main document with the main data source because the data records were empty or no data records matched your query options.

I adjusted as you advised so the line reads

If Err.Number = 5631 Then Err.Clear

I have re-run the mailmerge macro but this has not fixed the above runtime error popping up.

My macro works fine if there is more than one record, my problem is only if there is just one record it breaks/errors.
For example: If we have a list of 12 records for the day but the word doc I am wanting to save refers to only 1 or 3 entries, if we go into edit recipient list and only tick the ones we need we get that run time error.

If I add a filter to the full list so it only shows the entries we need rather than unticking them it will work BUT only if there are more than 1 entry.

In the meantime I have advised my colleagues if there is one entry just save as a pdf manually.