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Gas Valves for Commercial Boilers 101

Gas Valves for boilers Vent Valves Pilot Gas Valves

This article breaks down the most common gas valves used in commercial boiler systems, including manual shutoff valves, safety shutoff valves, and modulating gas control valves. It explains what each valve does, why it matters, and where it’s typically used, while highlighting common models contractors encounter in the field. The goal is to give you a practical understanding of how these valves work together to ensure safe, reliable, and efficient boiler operation — and what you should take away when selecting, servicing, or troubleshooting gas train components.

Term of the WeekGas Valves for Commercial Boilers

Industry Term of the Week

Combustion Valves

Manual Shutoff Valve

What it is: A hand-operated ball or plug valve.
Purpose:
  • Used to manually isolate gas for service.
  • Required ahead of the gas train and often at the burner.

Safety Shutoff Valves (SSOV) – Main Automatic Gas Valves

Important: These are the most important valves on the gas train.

What they are: Electrically operated valves (typically solenoid or motorized) that automatically open and close. 
Purpose:
  • Open only when the burner control proves safe conditions.
  • Close immediately if flame is lost or a fault occurs.
  • Prevent unburned gas from entering the combustion chamber.

A) Single-Stage (On/Off) Valves

  • Fully open or fully closed
  • Used on single-stage burners

B) Two-Stage Valves

  • Low-fire and high-fire positions
  • Used on staged burners

C) Double-Block-and-Bleed Configuration

  • Two safety shutoff valves in series
  • Bleed valve between the shutoff valves
  • Prevents downstream gas leakage if a valve fails

Common models: Honeywell, Kromschroder, Maxon

Modulating Gas Control Valve

What it is: A valve that adjusts gas flow proportionally (0–100%).
Purpose:
  • Used on fully modulating burners.
  • Controlled by a burner management system.
  • Matches fuel flow to load demand.
Signal types:
  • 4–20 mA
  • 0–10 V
  • Linkage from a servo motor

Common Manufacturers: Maxon/Eclipse, Honeywell, Kromschroder

Vent Valve ( Bleed Valve )

What it is: A small normally-open valve located between two SSOVs.
Purpose:
  • Vents trapped gas between safety valves when system is off.
  • Provides proof of tightness.
  • Required on many larger commercial boilers.

Common Manufacturers: Honeywell, Asco, GC Valves

Pilot Gas Valve

What it is: It is an electrically operated on/off valve that controls gas flow to the pilot burner.
How it works:
  • Normally closed
  • Opens only when energized by the burner management system
  • Closes immediately on flame failure or safety trip

It is typically much smaller than the main safety shutoff valves. 

Common Manufacturers: Asco, GC Valves

The Big Takeaway

    Big Picture for New Techs:

    Gas valves aren’t just about turning fuel on and off — they’re layered safety systems designed to prevent unsafe combustion, gas leaks, and catastrophic failure.

Remember: If one fails or trips, the burner shuts down — and it should.
Combustion Valves

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