buffalobill wrote:
not in buffalo ny, but if required by your local plumbing codes.

Ed wrote:
Should I put a back flow preventer or check valve on the water inlet on a
water heater ?

If it is required by code, it will be required at the house supply
inlet, usually where the service enters the house (unless it is part of
the meter). It won't specify that it is neededon the water heater.
Someone else pointed this out but I will add it again. If a check
valve is placed on the heater inlet, then an expansion tank should be
installed.

Harry K