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Test Thermal Expansion Bypass — Final Checks and System Purge

Beginner

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How to Replace a Well Pressure Tank · Step 10 of 10

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This test applies to open plumbing systems with a regulator that has a thermal expansion bypass. Close all faucets and trigger the hot water heater to begin a heating cycle. You can do this by briefly running hot water or by temporarily raising the thermostat setting. As the water heats, it expands, causing the pressure to rise. Watch the gauge. The pressure should rise but not exceed the municipal supply pressure by more than 10 PSI. In the video, the pressure rises from the 50 PSI static pressure to 95 PSI, which is only 5 PSI above the 90 PSI municipal pressure, confirming the bypass is working.

Goal: Verify thermal expansion bypass functionality

  • This test is for open water systems where the regulator has a built-in thermal expansion bypass. Closed systems require a separate thermal expansion tank.

Used in this video

  • Water Pressure Test Gauge (brand: Watts, Tool Type: Measuring Tools) — To monitor the pressure increase caused by thermal expansion.
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FAQs

What are the most critical safety steps I must take before beginning to replace my well pressure tank?

Absolutely always turn off the power to your well pump at the main electrical panel first. Then, fully drain the entire water system to relieve all pressure. This prevents electric shock, water damage, and injury from pressurized components.

How long should I expect this well pressure tank replacement to take, and what's the approximate material cost for a DIYer?

For a beginner, plan for 2-4 hours, assuming you have all tools and materials ready. The material cost, primarily for the new pressure tank and fittings, can range from $200 to $600, depending on the tank size and brand, plus a few dollars for tape and rags.

Why is correctly pre-charging the new well pressure tank so important, and what pressure should I set it to?

Pre-charging with air prevents the tank from becoming 'waterlogged' and ensures your pump cycles efficiently, extending its lifespan. Set the tank's air pressure (when empty) to 2 PSI below your well pump's 'cut-in' pressure (the pressure at which your pump turns on).

Which specialized tools are absolutely essential for replacing a well pressure tank, beyond basic household tools?

You'll definitely need a sturdy pipe wrench (like the 16-inch self-adjusting one mentioned) for plumbing connections, a tire pressure gauge to check the tank's pre-charge, and a water pressure gauge to monitor system pressure. Slip-joint pliers are also very helpful for various fittings.

Transcript
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This water pressure regulator has a built-in thermal expansion bypass. I've increased the temperature setting on my hot water heater and it is now heating and you can see that the pressure on the temperature test gauge is rising. Hot water expands in volume and increases the water supply system's pressure because I have an open system and a regulator with a thermal bypass. The excess pressure is absorbed by the municipal supply system. The manufacturer's specs say that the downstream pressure should not rise more than 10 pounds psi above the supply system pressure. The pressure has maxed out at 95 pounds. I know that my municipal pressure is 90 pounds. So we only have an increase of 5 pounds that passes the manufacturer's test and proves that the thermal bypass is working. If I wait a while eventually the pressure will drop back to the 50 pounds static pressure. To release the pressure quickly I'll open a cold water tap.

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