Came across a weird water heater issue that I could not figure out yesterday on a warranty inspection.
The homeowner had tried to use only one of his two water heaters for some reason and had discovered the problem. I confirmed the problem but was stumped to determine what exactly was going on.
Here is the setup:
Two water heaters are installed in the garage but are separated by finished wall so the plumbing between them is hidden.
When the inlet valve to unit 1 is turned off all fixtures in the home lose supply. AND Unit two loses supply. Suggesting to me initially that the units are plumbed in series.
When Unit 1 is turned on and heating all fixtures in the home have hot water. When unit 1 is not heating and unit 2 is heating no fixtures in the home have hot water.
The homeowner explained this when I arrived and turned off Unit 1’s burner and turned on Unit 2’s burner. Then we filled all of the bathtubs to exhaust the hot water supply and allowed unit 2 to heat up during the inspection. It heated properly and supplied hot water out of it’s TPR. But did not supply any to the fixtures in the home.
I suspect that Unit 2 is improperly tied into the plumbing system. But I cannot figure out how it could be on the hot water side (confirmed by losing pressure when the inlet valve was closed on unit 1) but not supply at least some hot water. Even if the inlet side dip tube was missing it should have provided some lukewarm water to a fixture after it had heated to 140 degrees and it provided NOTHING. The water at the fixtures was absolutely cold.
I referred it over to have a plumber look at it and will be following up to see what they find.