How to Measure inlet gas pressure of Navien tankless heater

Navien tankless water heaters are renowned for their energy efficiency and continuous hot water supply. However, to ensure the heater operates at its optimal level, it’s crucial to monitor and maintain the inlet gas pressure. This comprehensive guide will walk you through the process of measuring the inlet gas pressure for your Navien tankless heater. Whether you’re a homeowner or a professional installer, understanding this procedure is essential for the heater’s performance and longevity.

Why Measuring Inlet Gas Pressure Matters:

The inlet gas pressure is the force with which natural gas or propane enters your Navien tankless heater. This pressure is a critical factor because it directly impacts the heater’s ability to ignite and heat water efficiently. If the gas pressure is too low or too high, it can lead to issues like incomplete combustion, erratic heating, or even safety hazards.

Important Safety Note:

Before we dive into the step-by-step process, it’s vital to emphasize that working with gas systems should always be approached with caution. If you’re uncomfortable or inexperienced with gas-related tasks, it’s best to hire a qualified professional to perform this procedure. Gas leaks and mishandling can result in serious consequences.

What’s the Right Gas Pressure?

Gas pressure isn’t a one-size-fits-all thing. It depends on the type of gas your water heater uses. Here are the acceptable ranges:

  1. For natural gas-powered water heaters: The gas pressure should be between 3.5 and 10.5 inches of water column (WC).
  2. For water heaters using liquefied propane (LP) gas: The acceptable range is between 8.0 and 13 inches of WC.

These ranges are carefully determined by Navien by performing various tests to ensure your water heater works safely and efficiently. Going outside of these ranges can cause performance problems, shows error codes and safety hazards.

Safety When Testing Pressure

When it’s time to test the pressure of your gas supply piping system, there are important safety rules to follow:

  • If you’re testing at pressures higher than 1/2 psi (3.5 kPa), you must disconnect the appliance and its individual shutoff valve from the gas supply piping system.
  • When testing at pressures equal to or less than 1/2 psi (3.5 kPa), you should isolate the appliance from the gas supply piping system by closing its individual manual shutoff valve.

These rules are in place to prevent accidents and gas leaks during pressure testing.

How to measure inlet gas pressure in Navien tankless water heater

Shut Off the Gas Supply:

Locate the gas supply line leading to your Navien heater. There should be a manual gas shut-off valve along this line. Turn the valve to the “Off” position to stop the flow of gas to the heater.

Purge the Gas Line:

To ensure there’s no residual gas in the line, open a hot water faucet near the heater. Allow it to run until the water heater’s burner stops. This purges any remaining gas from the system.

Remove the front cover or panel:

Carefully remove the front cover of your Navien tankless heater. Use an appropriate screwdriver or wrench to loosen and remove the screws securing the cover in place. Once removed, set the cover aside.

Connect the Manometer:

locating pressure checking point on navien tankless water heater

Locate the pressure test point on the gas valve of your heater with the help of above image. This is typically a small port with a threaded cap. Remove the cap and attach the manometer to the test point. Ensure it is securely connected.

Restore Gas Supply:

Turn the manual gas shut-off valve back to the “ON” position. This will allow gas to flow to the manometer and the heater.

Check for Leaks:

While the gas supply is on, inspect the gas connections for any signs of leaks. You can do this by applying a soap and water solution to the connections. If you see bubbles forming, this indicates a gas leak. In this case, immediately turn off the gas supply and contact a professional for repairs.

Record the Gas Pressure:

With the gas supply restored and no leaks detected, Open multiple fixtures with high flow rates, such as bathtub and shower faucets. This will ramp up the water heater to its maximum firing rate. When the water heater reaches its maximum firing rate observe the manometer’s reading. The gas pressure should fall within the manufacturer’s recommended range for your specific Navien tankless heater model.

Remove the Manometer and Restore the Heater:

Once you’ve recorded the gas pressure, carefully detach the manometer from the test point. Replace the threaded cap on the gas valve. Put the front cover back on your Navien heater and secure it with the screws.


Measuring the inlet gas pressure of your Navien tankless heater is a crucial maintenance task that ensures your heater operates efficiently and safely. While we’ve outlined the steps for you, remember that gas-related work should be handled with care. If you’re uncertain or uncomfortable performing this procedure, it’s always wise to seek the assistance of a licensed professional. By maintaining proper gas pressure, you can enjoy uninterrupted hot water and extend the lifespan of your Navien tankless heater.

TanklessHelp Staff

TanklessHelp Staff has an experienced writers and researchers in the field of water heating technology. With a background in HVAC and plumbing, Tanklesshelp staff has in-depth knowledge in many types of waterheaters in America and Canada. They have a passion for educating homeowners and businesses on solving easy to hard repairs and guide them on how to maintain them to save money.

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