Gas line pressure check

What is going on

Checking gas inlet pressure on the C95 and C140 is done at the line pressure test port with a manometer, before you light the unit. It tells you whether the utility or piping is delivering what the boiler needs, both standing still and with the burner at full fire. Be careful with the gas side throughout. Make sure the supply is off before connecting anything, use only a bubble solution to check for leaks, and keep any ignition source well away from the work area.

Likely causes

• Static supply pressure outside the range in Table 8.1
• Pressure dropping too far at maximum fire from undersized piping or a restricted regulator
• Other appliances starving the line when they run
• Leaking test port after the check

Check in this order

1. Turn off the gas supply to the boiler.
2. Open the line pressure test port bleed screw about 1-1/2 turns.
3. Connect tubing to the test port and make sure both ends seal tight.
4. Open the gas supply and check for leaks with a bubble test (no open flame).
5. Read static pressure and compare with Table 8.1.
6. With other gas appliances running and the burner at maximum fire, check the pressure drop and compare with the minimum.
7. If pressure is out of range, have the gas utility correct supply pressure. The boiler gas valve cannot correct line pressure.
8. Close the bleed screw fully when finished and leak-check it with bubble solution.

More boiler guides

• 0-10 VDC input to modulate firing rate (Mode 5)
• Annual maintenance and inspection
• Blank display
• Boiler pressure keeps dropping / FILL shows
• Boiler shows FILL and will not fire
• Cleaning the combustion side of the heat exchanger