I have a shower that is run off the mains (combi boiler).
The shower just on certain days runs hot to cold and cold to hot.
There are no problems with hot water in the rest of the house and the heating works fine.
NO OTHER DHW OUTLET OPEN? (TAP, WASHING M/C OR DISHWASHER).
I FIND THAT ON COLD WINTER DAYS THE SHOWER IS MORE STABLE BECAUSE THE MAINS WATER IS VERY COLD AND IS EFFECTIVELY NOT OVER HEATED BY COMBI.
(BOILER STAYS ON, WATER CONSISTENTLY HOT).
ON WARMER SPRING/SUMMER DAYS, THE SHOWER IS MORE ERRATIC BECAUSE THE MAINS WATER IS WARMER AND IS HEATED MORE QUICKLY BY THE COMBI AND CONSEQUENTLY THE BOILER CYCLES OFF AND ON IN AN EFFORT TO DISSIPATE HEAT AWAY FROM BOILER.
(HOT WATER CANT GET AWAY QUICKLY ENOUGH FROM BOILER SO IT SHUTS DOWN UNTIL LOWER THAN PRESET DHW TEMPERATURE IS SENSED AND THE BOILER FIRES UP AGAIN).
IF CHECK/STOP VALVES ARE FITTED IN SHOWER SUPPLY PIPES, THEY CAN BE ADJUSTED SO THAT MORE OR LESS FLOW IS ACHEIVED IN EITHER THE HOT OR COLD SUPPLY TO THERMOSTATIC SHOWER VALVE.
AJUSTMENT HERE MAY HELP.
(THEY MAY NOT HAVE BEEN SET UP IN THIS MANNER TO START WITH).
IT COULD BE THE FIRST SIGNS OF THE DIVERTER DIAPHRAGM FAILING.
IT IS MORE NOTICEBLE IN THE SHOWER/BATH BECAUSE YOU ARE IN IT FOR LONGER PERIODS COMPARED TO FILLING A SINK OR DISH.
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