water pressure continually rises on a baxi 105e?

I have two faults on my Baxi 105 E
The water pressure continually rises although the filler loop is disconnected. Also the pressure release valve drips even though the pressure is not high enough for it to operate.
I believe the plate heat exchanger could be the problem, however could it be something else? As far as te pressure release valve fault it is more likely just needing replaced

Brian
December 2008