There is a lot of confusion here, Is the vent metal? If so the tank is atmospheric venting no blower on the appliance. If the water heater has a blower and only one pipe exiting the building then it is a power vent.
If the vent is atmospheric and metal (either single wall or double wall, the problem is one or two issues:
1) The developed vent length outside is condensing water vapor and becoming ice blockage or it takes a lot of heat to prime the stack and get the vent to draw in the dilution air to force a NATURAL DRAFT UP the Stack.

2) If it is a power vent the fan would over come the cold air back drafting down the vent into the house.

3) If it is a natural draft and the cold air is entering the house it is more than likely because the house pressure is going negative because of other fans exhausting to the out side. The most common problem is wood burning fireplace or wood stove operating and creating a negative pressure.

If the vent is Plastic (white or grey) the the appliance is a condensing (high efficiency unit),

It sounds like the vent rising as high as stated is to long with too much heat loss and not allowing the vent to get hot enough to establish draft, the entire outside piping should be insulated to solve the issue. (This will not solve the issue if the house is going negative, only installing a proper combustion air supply will solve that issue .

If the piping is plastic and freezing Frostfree Venting has a product to solve that problem
Lester

Lester, when replying to a posting, click the orange "Post Reply" bar at the bottom right corner of the post you are responding to. This will keep your response with the thread.

I cannot find ANY previous query that corresponds to your "solution".