Sounds like the system is blocked so the water is not circulating .if the system is blocked which what it sounds like you will have to get it power flushed .if it was just the pressure problem I'd say it could be just the vessel blocked or the bladder buggerd but as some of your rads arnt...
Basically the boiler is reaching temp to quick because it can't get rid of its heat now because the right hand pipe is getting hot for about two mtrs it lookls like the water isn't moving you need to check the pump because they have got a habit of throwing the impeller so it sounds like the pump...