Halstead quattro diverter valve?

Hi,

I have a Halstead quattro.
I had the diverter valve replaced in Dec 2013 but had found that recently there is water coming out of the top of the diverter underneath the micro switch.
This only happens when the boiler is not in operation , also if i cut the cold feed to the boiler this stops too.I assume this is only a hot water problem.
How do i go about fixing this ?