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Water heater expansion tanks
Quick answer
Expansion tanks absorb the pressure that builds as water heats and expands. California requires one on new installs, and they protect your heater and plumbing.
Your pressure regulator is the first line of defense against pressure surges, and the expansion tank is the second. High pressure makes appliances and pipes fail early, and early failures put water where you don't want it.
If the regulator isn't working, the expansion tank can't do its job. Change them together. With a working regulator, an expansion tank prevents leaky faucets, toilets that refill on their own, broken icemakers, damaged dishwashers and struggling RO systems, and usually stops water hammer.
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Expansion tank service