plumbing

[GregOConnor]

wow you are the first to not call it a hot-water heater. I'll go with Chuck but add that an inlet restriction would be possible also. The other thing that may be a long shot, and I am not sure if it is possible to mix up,, but if you are using the engine heat exchange ,,,did you hook the potable-fresh in and out to the storage tank? or in error to the radiator fluid path?
both paths are continuous and independent but the potable fresh water path has the larger storage and the blow off valve.
You may understand all this but I for one was surprised that the engine heated the water heater tank while the bus was running down the road