On Thu, 5 Nov 2015 01:21:35 -0000, bm wrote:

Clean the tops well and leave a damp cloth over them for a few
hours,
if your water is hard soak with dilute lime scale remover. Look
carefully for a recess along the edge of the cap into which insert
a
small bluntish flat blade screwdriver.

Or the point of a scriber.

Scriber to remove cack along the join but not for pushing
in/levering. The pressures at points of contact are too high and the
plastic will deform.
The ideal tool is something thin, stiff and hard but not hard like
metal, hard like hard plastic. Trouble is thin, hard plastic tends
not to be very stiff.

--
Cheers
Dave.