Ban you unsympathetic s*d.
The poor devil will smell awful in few days.
Arkroyal, you are probably in a hard water area and the flow is being restricted by limescale build up as advertised on the television (washing machines and Calgon)
There maybe nothing for it but to replace the unit.
Start by removing shower head. Does water now flow? If yes, clean shower head in a 10:1 dilution of brick cleaning acid in water (add acid to water not the other way round). If not, buy new shower.
Is the shower still under guarantee?
if it is call customer service, if its not, you got nothing to lose by taking the filter valve off and blowing it through
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