Make sure your cylinder stat is set high enough .
Usually 60.
With just the hot water on at the programmer, increase the stat setting on the cylinder. Do you know what the pump is? If you do, you should hear it kick in when you turn up the stat. It's usually sighted near the cylinder.
If you can't hear or feel the pump running, you could have a faulty stat or loose wire in the stat or 10 way box. (Electrics) Your 3 port valve may also be seized in ch only position or the actuator (motor) on top may have failed? 3 port valve next to cylinder too.
Unless you know how to test it, recommend you contact a local CORGI bloke.
Baz (CORGI Eng), May 2007