Can anyone solve this mystery? Just had an unvented cylinder installed and consequently needed to change a fully working power shower for a mixer shower. I isolated the shower using two chrome isolating valves under the shower tray; removed the power shower; changed the pipework in the shower cubicle and then turned the two isolating valves back on to check for leaks before fixing the Mixer. Cold supply was fine but I have NO water from the hot supply! Prior to the fitting of the unvented cylinder the (power) shower was working fine. I have also noticed that the shower at the rear of the house (utility room) on ground floor also now has no hot water flow. This shower was also previously working fine. I assumed at first that the valve on the Power Shower supply had failed but now I have discovered a very similar (identical?) problem with the second shower it seems unlikely. All other H&C outlets work fine. The two showers are plumbed separately . Any ideas would be appreciated.