Hello - when I turn on my shower water initially comes out for about 5 seconds and then slows to a trickle and virtually stops. I think it is connected to the balancing somehow as previously when this happened I adjusted the valve connected to the shower and the water come out normally. However as a result of my tampering water backed up through the pipe leading to the tank in the loft and came out of the overflow. Thats why I adjusted the valve again to stop that happening. Can anyone advise me as to how I can get water coming out of my shower without it backing up the pipe?