With so little information provided it is almost impossible to give you an answer
Quote = does not heat the water in the tank in
"hotpress" not sure what this means
Is the boiler even piped up to the cylinder ?
if so the problem could be any one of these =
Blocked pipework around the cylinder area or coil in cylinder. (not unusual on the domestic return if cold feed is branched in here)
Is there an air vent on the top pipe going into the
SIDE of the cylinder ? try venting it.
Balancing valve balanced down to much (if one is fitted)
3 port valve or hot water zone valve faulty (is it powering open)
Cylinder thermostat faulty
programmer faulty.