Gas orifice

If you smell gas, leave the building and call FortisBC at 1-800-663-9911 or 911 from outside. Never drill, ream, file or enlarge a gas orifice, and never swap one for a part from a different boiler. The orifice is a metering device for a fuel gas, and altering it changes the input rate, the flame and the safety of the appliance.

In British Columbia, replacing orifices, converting a boiler between natural gas and propane, or re-rating for altitude is licensed gas work under Technical Safety BC. The contractor performs the work under permit and confirms the result with combustion testing.

A boiler that has been fired with the wrong orifices can soot, overheat, produce carbon monoxide or fail to light reliably. If you suspect the wrong parts are installed, stop using the boiler and have it inspected rather than continuing to run it.

Gas arrives at the burner through an orifice: a small, precisely machined hole that controls how much fuel flows at the manifold pressure the boiler was designed for. Each burner on an atmospheric boiler has its own orifice; on a premix condensing boiler the gas is metered into the venturi, and the equivalent calibration is done through the gas valve's throttle and offset settings.

The orifice size is not universal. Natural gas and propane need different sizes because the gases carry different energy per cubic foot, and altitude changes the amount of air available for combustion. Slant/Fin's Sentry manual prints separate orifice numbers for natural gas and propane and applies a four-percent reduction in input for each 1,000 feet of elevation above sea level, with the factory orifice installed for sea level unless the local authority specifies otherwise.

Because the orifice is the burner's fuel meter, it also shapes the flame. Crown's Bermuda manual instructs the installer to seat the front of every burner completely on its orifice, and lists an incorrectly sized or drilled burner orifice among the causes of carbon-monoxide production.

Orifices clog. Dust, pipe scale, thread sealant and debris from the gas line can partially block the opening, starving one burner while the rest burn normally. A partly blocked orifice produces a weak, lazy flame at that burner, delayed ignition, or a flame that flashes back and burns at the orifice instead of on the burner surface.

Slant/Fin's Sentry troubleshooting table lists obstruction at the main burner orifice as a cause of burner problems and instructs the technician to check, clean and reinstall, and it lists burrs on the orifice or improperly drilled orifice plugs among the causes of flashback. Those entries describe the two failure families: contamination, which can be cleaned, and damage or substitution, which means the part must be replaced with the correct one.

A wrong orifice is the quiet failure. It may light and run, but at the wrong input, which shows up as sooting, poor efficiency, short cycling or high CO. On conversions between natural gas and propane, the manufacturer's conversion kit and rating-plate data are what make the change safe; nothing about the work is generic.

You can note the symptoms without opening anything: soot around the burner area, a yellow or lifting flame seen through a sight glass, popping or delayed ignition, and repeated flame or ignition alerts. Report any recent gas work or a conversion you were not told about, because that history matters.

Never clean an orifice with a wire, drill bit or pin, and never attempt to re-drill one. The hole size is measured in fractions of a millimetre and any scratch changes the gas flow. Keep the boiler area clear and make sure the vent and combustion-air paths are unobstructed.

If the boiler smells of gas at any point, leave and call FortisBC before doing anything else. If it runs but behaves oddly after gas work, ask for the installing contractor to verify the orifices and combustion rather than living with it.

A technician verifies the orifice number against the model, fuel and altitude data in the manual and on the rating plate before touching the burner. Where contamination is the problem, the orifice and burner are cleaned following the manufacturer's procedure, and the technician confirms that the burner seats correctly on the orifice the way Crown's manual describes.

The repair is then proven, not assumed. Gas input is checked against the rating plate, manifold pressure is measured at the gas valve, and combustion is analysed at the flue. Slant/Fin's Sentry instructions treat the high-altitude orifice table as part of the boiler's specification, so a technician re-rating a boiler above sea level uses that data and records the change.

Orifice work is small, precise and entirely gas-side, which is why it belongs to a licensed contractor. If your boiler was converted, moved or re-rated, or if it is sooting or popping, call ROMA Heating & Cooling to have the gas side verified.