Shower runs extremely hot for about 15 seconds, then next to cold unless you lower shower head to floor and then marginally warmer for a few seconds. I have replaced the mechanical parts for the Mira 88 shower and that appears to work perfectly. I notice the hot water on leaving the top of the cylinder passes to both the bath and sink after passing the shower, and both sink and bath run hot perfectly. I also have discovered through getting very wet and cold that with the shower mechanical parts removed water pours happily out of the cold side, but only intermittently from the hot side. The hot exit pipe from the top of the cylinder that feeds the sink, bath and shower also has a T connection going up to a vent. The shower head is 2ft 6 inches above the sink taps and even higher above the bath taps. Is there a link here? Any advice welcome.