About 12 years ago, I had an old water heater replaced in Virginia without an expansion tank. Within a few days, I noticed a small amount of water in the drain pan. It was because the new relief valve was occasionally tripping and releasing water. That means that the water pressure was exceeding 150 psi. The contractor said that the relief valve on the old water heater was totally clogged with sediment, so it did not function at all. The contractor installed an expansion tank, and I never had the problem again.
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