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