If all else fails, replace this black box with a conventional CH junction
box in order to connect the programmer, boiler, pump and room stat in the
normal way. As I said before, you won't then be able to use the cyl stat -
unless you add a zone valve and convert it to a C-Plan system.

It is easy enough to use the cylinder stat without the zone valve, even
though it doesn't provide temperature limiting when in CH mode. The HW On
signal is just filtered through the cylinder stat before it goes on to turn
the boiler on.

Christian.