boiler pressure problem?

Sounds very much like the selector switch is not working or one of the CH demand controls, ext thermostat for example, as nothing happens at all, i.e. no pump or fan starting which you would be able to hear and no error codes implying the CH cycle has been attempted and then failed.
Of course, this will not solve the de-pressurising fault but that can be addressed after we have established the CH fault. Be sure you re-pressurize the system to recommended 1.0 to 1.5 bar before attempting to operate the CH or DHW.
Be sure to post back with an update.

Robert
October 2010

Assuming you do not have the manual, its here:
http://vokera.co.uk/wpcontent/uploads/2009/04/linea_24_28_users_instructions.pdf
"With the control switch set to off/reset the boiler still fires up and we get hot water", refer to manual and identify which control switch you are referring to, strange that the boiler fires up with hot water if switched off!
Go through the first few pages to ensure you are following the correct procedure to switch on heating, external thermostat turned up high, PRV's on each rad turned up high (if fitted), temp setting on boiler up high, timer?, select heating & water.
Read 2nd section of 1.2, as per your comments about sticking valve.
Then read through the whole manual to familiarise yourself with all functions.
Sounds very much like the selector switch is at fault, i.e. Section 1.1 and Fig.2. Stuck on hot water only, if you change the position of the switch it is still selected to hot water. Can the switch be pulled off from the front? to expose the control behind, can the switch then be turned manually, now try heating. Is the plastic retainer on the inside of the switch you have taken off, if poss., broken so not holding onto the control to change selection?
Keep us posted.

Robert
October 2010

The prv is not dripping. Nothing happens when heating is in demand, it has been off for several months, would the lack of use cause the valve to stick? Im still at a loss as to pressure drop. With the control switch set to off/reset the boiler still fires up and we get hot water. thanks

adam
October 2010

Wouldn't imagine you are losing pressure due to a leak under floor or walls as you would have signs of a leak.
Is the PRV dripping? It should have a pipe connected to it and terminated outside or somewhere safe.
Does anything happen when you demand CH.
Possible 3 way divertor valve stuck closed/open so only DHW but also possible PCB at fault.
Need more details regarding CH attempting to start up.

Robert
October 2010