Glow worm compact 100e, leaking water on prv?

I have the above mentioned boiler and over the past week has started leaking water out the prv (pressure relief valve). When the boiler is cold i fill it up to just over 1bar then when the heating starts up all is fine until the pressure reads about 2.8bar then it starts to drip out the prv until it reads about 2bar. Then when the heating is off and gone stone cold again it only reads 0.3 bar. Why is my boiler releasing the water? Thanks.
Also check out my other problem titled
"glow worm compact 100e warm (not hot) water."