Isolating power and gas is the first, most important step before cleaning burners, opening a gas train, or touching any ignition components. Done right, it prevents unexpected ignition, fuel release, shock, and equipment damage. This post gives technicians a precise, repeatable procedure you can embed in your SOPs.
What “Isolate Power/Gas” Means
- Electrical isolation: The appliance cannot energize—no fans, no spark/hot-surface ignition, no control power.
- Gas isolation: The appliance cannot receive fuel—manual shutoff valves are closed and any residual pressure is safely relieved before you open anything.
Why both? Many appliances use electronic ignition. Leaving power on while exposing gas passages invites an unexpected spark during a brief gas release—a serious hazard.
Step-by-Step Isolation
- Prepare & Cool
- Announce the shutdown and let hot surfaces cool.
- Keep general ventilation ON (exhaust & make-up air) so any trace gas dissipates.
- Electrical Isolation
- Unplug the appliance, or open the local disconnect / breaker feeding it.
- Lock & tag the plug/disconnect/breaker.
- Verify zero energy: attempt to power the unit; controls, fans, and igniters must remain OFF. If accessible, confirm 0 VAC at appliance terminals or that the control transformer is de-energized.
- Gas Isolation
- Turn the combination gas valve to OFF (ON–PILOT–OFF types).
- Close the appliance manual shutoff valve (ball valve) just upstream of the unit. If required, also close the branch service valve further upstream.
- Tag closed valves.
- Prove Zero Gas / Relieve Residual
- Connect a manometer to the manifold test port; pressure should decay toward 0″ w.c.
- If a small bleed is needed, briefly crack the test port (or a union) to release residual pressure—minimize release and keep ventilation running. Retighten and leak-check afterward.
- Extinguish any standing pilot and allow the thermocouple to cool.
- Confirm no persistent gas with a combustible gas detector (or at minimum, no odor).
- Confirm Zero-Energy State
- Attempt a start with power still locked out—there should be no ignition attempts and no gas flow.
- Only then remove burners/venturi or open gas passages for cleaning/repair.
Reassembly & Return to Service (Reverse Order)
- Refit parts; tighten all fittings to spec.
- Leak test every disturbed joint with approved leak solution—no bubbles allowed.
- Open gas slowly at the manual valve; watch inlet/manifold pressure on your manometer.
- Relight per OEM instructions (pilot first if applicable), then restore power (remove locks/tags).
- Verify ignition sequence, dynamic manifold pressure, flame quality (sharp blue cones, no lifting), and no leaks.
- Record readings and outcomes in your service log.
Common Mistakes to Avoid
- Shutting only the thermostat and assuming gas is isolated—it isn’t. Always close the manual shutoff valve.
- Leaving power ON so a spark module fires while gas paths are open.
- Bleeding a large amount of gas into the room—keep ventilation on and minimize any release.
- Skipping the post-work leak test and dynamic pressure check under high fire.
Quick Field Checklist
- ☐ Power unplugged or disconnect/breaker open, locked & tagged
- ☐ Combination gas valve OFF; manual shutoff CLOSED (tagged)
- ☐ Manifold pressure at ~0″ w.c.; residual safely relieved; no gas detected
- ☐ Burners/venturi cleaned; parts reassembled correctly
- ☐ All disturbed joints leak-tested (no bubbles)
- ☐ Dynamic inlet/manifold pressures within OEM spec; flame blue & stable
- ☐ Readings logged; unit returned to service
Safety & Compliance
Always follow manufacturer instructions, local codes, and your company’s safety policy. If at any point you detect gas or an unexpected attempt to energize, stop, ventilate, and reassess isolation before proceeding.