Signs the expansion tank has failed
- The relief valve on the water heater drips or discharges
- Tapping the tank sounds solid all the way up (waterlogged)
- Rust, weeping or a leak at the tank or its connection
- Pressure spikes: banging pipes, or toilets that refill on their own
- A tank that is years older than the heater it serves
How we handle it
- Measure the house pressure
A gauge on a hose bib shows the static pressure and the spike when the heater runs.
- Test the tank
We check the air pre-charge and whether the bladder has failed and let water into the air side.
- Recharge or replace
A tank that has only lost air can sometimes be recharged. A waterlogged or leaking tank is replaced, sized for the heater and the house pressure.
- Set and support it
The pre-charge is set to match your water pressure and the tank is properly supported, then we run the heater and check the relief valve stays shut.
Why San Antonio homes need them
Many houses here have a pressure reducing valve, a backflow preventer or a check valve at the meter. Each of those makes the plumbing a closed system, so the extra water from heating cannot push back into the street. Plumbing codes require thermal expansion control on a closed system, and with high street pressure in much of the city a failed tank quickly shows up as a dripping relief valve and stressed fittings.
Expansion tank or pressure reducing valve?
They do different jobs and often work together. The pressure reducing valve (PRV) lowers the pressure coming in from the street. The expansion tank absorbs the rise in pressure when the heater warms the water. A failing PRV lets street pressure into the house; a failing expansion tank lets heating spikes through. We test both, because replacing one when the other is at fault does not fix anything.
What a failed tank costs you
Each time the heater runs, pressure climbs. That pushes the relief valve open, wears the fill valves in your toilets, and strains the water heater, supply lines and fittings. A failed expansion tank is a small repair that protects much more expensive parts — see water heater repair and water heater maintenance.
What it costs
It depends on what the job turns out to need, so we diagnose first. Your plumber then gives you an upfront price, and you approve it before anything starts.
Questions people ask
Do I really need an expansion tank?
If your house has a pressure reducing valve, a backflow preventer or a check valve, it is a closed system and needs thermal expansion control. Many water heater installations in San Antonio fall into that category.
How long does an expansion tank last?
Often five to ten years. The bladder inside eventually fails and the tank fills with water. Replacing it along with the water heater makes sense when both are the same age.
Can you replace just the tank?
Yes. It is a short job on its own, and we check the house pressure and relief valve at the same time so the new tank is set correctly.