Expansion Tank Repair & Installation in San Antonio

Expansion Tank Repair, Replacement and Installation

CSW checks existing expansion tanks, replaces tanks that need it and installs new expansion tanks, including as part of a water heater replacement. The plumbing work is performed in-house under RMP #46592, and you get a free written, itemized estimate before work starts.

• Expansion tank checks on existing water heaters
• Expansion tank replacement
• New expansion tank installation, including with a water heater replacement
• Connections verified against current plumbing code

When San Antonio Code Requires a Thermal Expansion Tank

San Antonio adopted the 2024 International Plumbing Code with local amendments in City Code Chapter 10, Sec. 10-82 (Ordinance 2025-01-30-0075). Amended Section 607.3 says that where a storage water heater is supplied with cold water that passes through an on-site check valve, pressure reducing valve or backflow preventer, a thermal expansion tank shall be connected to the water heater cold water supply pipe downstream of all check valves, pressure reducing valves and backflow preventers. San Antonio also limits thermal expansion control to expansion tanks, under its 1998 water conservation requirements (Ordinance 89128).

• An on-site check valve on the water heater's cold water supply
• A pressure-reducing valve (PRV) on the cold water supply
• A backflow preventer on the cold water supply

Expansion Tanks, PRVs and SAWS Water Pressure

IPC Section 604.8 requires an approved pressure-reducing valve where static water pressure in a building exceeds 80 psi, so the building's distribution piping stays at or below 80 psi. SAWS says water pressure in its service area can range from 35 to 175 pounds, that high pressure can be controlled by a PRV installed on the property owner's side of the water meter, and that the recommended maximum is 80 pounds. Because a PRV on the cold supply is one of the conditions in San Antonio's amended IPC 607.3, a home with a PRV and a storage water heater needs an expansion tank downstream of the PRV, sized so the system stays within Section 604.8.

Signs to Have Your Expansion Tank Checked

InterNACHI's inspection guidance says an expansion tank should be checked for proper location and support, corrosion and leakage, and that a horizontally hung tank needs additional support to reduce stress on the piping. Have the tank and its connections looked at if you notice any of these:

• Water, dampness or drips at the expansion tank or its connections
• Rust or corrosion on the tank or its fittings
• A tank hanging from the pipe without support
• A storage water heater on a supply with a check valve, PRV or backflow preventer but no expansion tank

Expansion Tank vs. the T&P Relief Valve

An expansion tank and the water heater's temperature and pressure (T&P) relief valve do different jobs. The expansion tank absorbs the normal increase in water volume as water heats, using an air cushion behind a bladder. The T&P relief valve is the safety device that opens and discharges water if pressure or temperature gets too high; InterNACHI cites 150 psi or 210°F. InterNACHI is clear that an expansion tank is not a substitute for a T&P valve, so the relief valve should never be removed, plugged or bypassed.

How an Expansion Tank Visit Works

We look at the water heater, its cold water supply and the valves on it, and the existing tank if there is one, then explain what we find and give you a written, itemized estimate. When a tank is needed or being replaced, we install it on the cold water supply downstream of any check valves, PRVs and backflow preventers and verify the connections meet current plumbing code. On a water heater replacement, installing the expansion tank and verifying code is part of the installation step.

• Inspect the water heater, cold supply valves and any existing tank
• Written, itemized estimate before work starts
• Install or replace the expansion tank where it is needed
• Verify all connections meet current plumbing code