IPC · 2024 International Plumbing Code
§607 · Thermal expansion control
Effective in IPC 2024.
Plain-English explainer
607 requires a listed expansion tank or an equivalent control where a backflow preventer, a pressure reducer, or a check valve can trap pressure on the hot-water side, so the expanded water is absorbed and the water heater and supply piping are protected. The drafter cites it whenever a permit pulls in a closed-pressure-loop water heater.
Why inspectors flag this
A closed water heater on a supply with a backflow preventer and no expansion tank is the canonical 607 failure; the drafter surfaces the rule so the spec includes the expansion tank before the inspector walks the rough-in.
As quoted in the code: Where a backflow preventer, a pressure reducer, or a check valve can trap pressure on the hot-water side, a listed expansion tank or an equivalent control is installed to absorb the expanded water and protect the water heater and the supply piping.
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