Carolyn wrote:
Snip
Pretty much what I thought, except that I haven`t altered the way the pipes
feed to the washing machine & it was ok before the combi was fitted.. Perhaps
the plumber disconnected/reconnected for some reason..? I will certainly have a look
when I`m able to access the back of the machine(not an easy job!)
Thanks for all your replies

The piping to the washing machine (from the combi) may be shorter than
the piping from the hot water tank was.
This means that when it draws water to rinse, it gets hot water, rather
than most of it being stuff that's sat in the pipe for half an hour and
gone cold since the fill.
A diagnostic should be to do a boilwash.
If it takes a long time to raise temp, and starts out cold, when it
should be taking in hot water, then it's almost certain.
(barring a maxwells demon infection)