Descaling Plate Heat Exchanger for Pulsa Coil Class A

Hi Mike & all,
I have a 2 year old pulsa coil class A installed in my flat and over the past 3 months the hot water pressure has gradually dropped (cold water still good pressure), I suspect that the heat exchanger is clogged with limescale (live in an area with extreme hard water). Do you have a brief guide on how to descale the heat exchanger (including disconnection, & all)
many thanks
Aminu