Pressure test the gas supply

What is going on

Most of the time a gas line gets pressure tested on a new install or after piping changes, and the boiler gets caught in the middle of it. The NTI TRX150 gas valve can only take so much. If the line test goes above 1/2 psi (14 in WC), the boiler and its shutoff valve have to be physically disconnected from the line. At or below 1/2 psi (3.5 kPa), closing the boiler's manual shutoff valve isolates it. Overpressure can damage the gas valve internals, and that is how you end up with a fire or an injury later, sometimes without any sign of trouble at the time of the test.

Likely causes

• Test pressure above the gas valve limit of 1/2 psi
• Boiler and shutoff valve left connected to the line during a high pressure test
• Manual shutoff valve closed but leaking by, so pressure reaches the gas valve anyway
• Test started before everyone on site knew the boiler was already piped in

Check in this order

1. Confirm the planned test pressure first and decide whether it is above or at or below 1/2 psi (3.5 kPa).
2. For tests at or below 1/2 psi, close the boiler's manual gas shutoff valve to isolate it.
3. For tests above 1/2 psi, disconnect the boiler and its shutoff valve from the line and cap the open pipe.
4. Watch the gauge for a few minutes and leak-check every joint with approved leak detector solution, never a flame.
5. Bleed the test pressure down slowly before reconnecting anything.
6. Do not fire the boiler until all connections are made and the heat exchanger is full of water.
7. Have a licensed gas fitter do the test and the reconnection, and leak-check the boiler connection after reopening the valve.

More boiler guides

• Access the low voltage wiring connections
• Blocking errors versus lockout errors
• Blower not running
• Blower runs at high speed with burner off
• Boiler bangs or hisses; Lockout 81 delta T
• Burner not running on a call for heat