Cold Water when it should be HOT

I have a circulating pump on my hot water heater yet occasionally when I use the faucet (single handle style with an anti scald-valve) in the bathroom that is farthest from the water heater even if I turn the faucet on hot only for the first few seconds the water is ice cold. This doesn't happen all of the time but often enough that it is becoming a nuisance. This problem doesn't occur in the other bathrooms.

water

Your check valve could have broken which would allow the cool water at the bottom of the water heater to flow back to the last fixture before the hot water circulator connection, which could be that shower.