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This is a toilet mixing valve image

A toilet Mixing Valve
This is what many toilet mixing valves look like, it has a hot water inlet, a cold water inlet and a mixed outlet that goes to the toilets only.
The amount of hot and cold water mixed water line can be adjusted by the two valves on either side of the mixed water line.
This type of mixing valve can fail, this is why it needs to be installed in an assessable location, when put into wall or other places, it makes it impossible to find and replace. chick here