Shower unit has been working well since installing it 4 years ago, it is not a power shower.
Without warning the water output pressure has dropped to about 25%, as far as I know it is fixed to a mains input and water pressure to washing machine, taps etc are all normal - my WC cistern refill slowed similarly 6 weeks ago and still refills very slowly, but this may be a red herring.
Any suggestions/help would be great thanks.