I have a 5 year old Triton LP shower. Hot water is fine but cold water is a trickle. I have tried opening/closing hot and cold water feeds to clear any blockages etc but to no avail. I have looked in the loft and traced the cold water pipe to a big plastic tank. I dont know if this is the right one because when the shower runs, no water leaves this tank but that might be because the pipe is blocked. This tank doesnt have any sort of ball joint for overflow so I could be looking in the wrong tank. I am a complete beginner at this so would appreciate any suggestions to reinstate the cold water flow to this shower?