Appliance startup and manifold pressure. Episode seven of the Gas Service Animated series. Bringing a gas appliance to life the right way: survey, leak check, purge, light, measure, and prove.

Before any flame, the code lays out a survey. The piping has to be complete, inspected, and pressure tested before it ever carries gas. The appliance must be connected the way its manufacturer says, with its shutoff valve and connector in place. The venting must be assembled and attached, and the combustion air openings the appliance depends on must actually exist. Only when the whole installation is ready does startup begin.

With gas on but before any light-up, every appliance connection and valve gets checked for leakage. The tools are a leak detection solution that bubbles at an escaping fitting, or a listed electronic gas detector. The code is blunt about the one method that is forbidden: a flame shall never be used to hunt for leaks. Find bubbles, fix the joint, and check it again before moving on.

A new gas line is full of air, and a burner fed with air simply will not light. So the line is purged: valves to other sections closed, gas admitted, and each outlet cleared one at a time, starting with the one nearest the meter. The tech verifies gas is actually present at each outlet before moving to the next, and never trusts smell alone to decide. How and where that displaced air goes is governed by the code's purging rules and your company's procedures.

Now the light-up. In a standing pilot system, a small pilot flame heats a sensor, and that tiny signal holds the safety valve open. Only a proved pilot lets the main valve open and feed the burners. Electronic systems do the same job with a spark or a glowing hot surface igniter, plus a flame sensor that must prove the burner within seconds or shut the gas off. Either way the rule is identical: no proof of flame, no gas.

With the burner running, we measure manifold pressure: the pressure in the small chamber that feeds the burner orifices. A manometer connects to the manifold pressure tap, and for natural gas the nameplate typically calls for about three and a half inches of water column. Watch the reading settle onto the nameplate value. If it is off, the adjustment happens at the appliance pressure regulator, following the manufacturer's instructions — never by guesswork.

Pressure alone does not prove the input, so we clock the meter. With every other appliance off, time one revolution of the meter test dial, convert to cubic feet per hour, and multiply by the heating value of the gas. The answer has to match the nameplate. Firing above the nameplate rating is prohibited by the code, and an underfired appliance runs poorly and can condense in its vent. The nameplate is the target, not a suggestion.

A running burner still has to prove its vent. The code says a draft hood appliance shows no spillage after main burner operation with the house at its worst case: the envelope complete, combustion air openings in place, and every exhaust fan and air moving system running. After five minutes of main burner operation, the tech checks the draft hood relief opening, using a mirror, a smoke source, or whatever the company procedure calls for. Flue gases rolling out of the relief opening instead of rising up the vent means stop and investigate.

Before leaving, the tech walks the whole result. Burner flames are stable and blue, with no lifting, floating, or flashback. Controls cycle the appliance on and off cleanly, and the safety shutoff proves out. The vent shows no spillage after five minutes, and the clocked input matches the nameplate. Then the customer gets a walkthrough, and the operating instructions stay in plain sight near the appliance.

Startup in one breath. Check the connections with solution or instrument, never a flame. Purge the air and prove gas at each outlet. Light and prove the flame, set the manifold to the nameplate, clock the input, and prove the vent in the worst case. Next episode: Type B vents and connectors, the highway that carries the flue gases out.