Have to manually re-light pilot to restart each heating cycle [gas water heater ]

Need more information, you mean that the pilot doesn't stay on and you have to manually re-light, if that is the case then you have problem with your thermocouple, please come back and we will tell what needs to be done, Thanks.

John

Hi warbird and welcome, John is more than likely on the right track, but if this is a FVIR heater it could be as simple as the filter dirty and the one burn using up all the O2. Is yours a FVIR?

Also the pilot may be getting blown out by a backdraft. After you light it watch it for sveral minutes. Have some one else open and close an outside door and/or window. Turn the heat up on your furnace, do any of these things create a backdraft?