ariston boiler - dangerous? Turn off heating?

My Ariston boiler heats water on demand and central heating.
The boiler keeps coming on and heating up the radiators even though I don't want it to. The pressure has gone into 3-4 bar which is too high also.
Is this dangerous and how do I prevent heating coming on?
(There is a small clock face on the controls with thin 'pins' to pull out for when you want the heating on - I pushed all the pins in which I take to mean it should be off all the time. There is also a small switch beside this to choose heating and water, just water, or off - I put it to off). There are two other lights with buttons below, one of these shows a radiator but as this is next to the pilot light I am worried to press it as I don't know what it's for.
Any help appreciated as am v. worried about the pressure/ safety and is also boiling!

Liz
July 2008