My shower is plumbed to the mains ie hot tank and cold tank in loft. Turned on (by tap that looks much like a hot/cold water tap) but when I went to turn it off the tap was very stiff & I couldn't get the water to stop. Hubby had to turn off but when turned shower tap back on the pressure of water coming out of shower head was a good bit reduced. Took head off and cleaned out but made no difference. Can you advise what to do?