A kitchen that loses hot water at the start of a dinner service. A hotel laundry room that goes cold halfway through the morning cycle. A school kitchen that fails a health inspection because it could not reach sanitizing temperatures. In almost every one of these scenarios, the culprit turns out to be something surprisingly small: pilot light problems on a commercial gas water heater.
Troubleshooting Pilot Light Problems in Commercial Water Heaters
The pilot light is the ignition source for the entire heating system. When it fails (whether it will not light, will not stay lit, or keeps going out under normal operating conditions), the water heater stops producing hot water until someone figures out why. This guide walks through the most common causes of pilot light problems in commercial settings, what to check first, and when to call in a professional.
How a Pilot Light System Actually Works
Before troubleshooting, it helps to understand what the pilot light is doing and what keeps it running.
In a standing pilot system (the type found on most traditional commercial gas water heaters), a small, continuously burning flame sits at the base of the burner assembly. When the thermostat calls for heat, the main gas valve opens, and the burner ignites from that standing flame. A thermocouple (or thermopile) monitors the pilot flame. It sends a small electrical signal to the gas valve, confirming the flame is present. If that signal drops, the gas valve closes automatically as a safety measure.
Newer commercial units use an intermittent ignition device (IID) instead of a standing pilot. With IID systems, the pilot lights only when the burner needs to fire, reducing standby gas consumption. Troubleshooting steps differ slightly between the two, so it is worth knowing which system your unit uses before you start.
The American Gas Association publishes installation and safety standards that govern the design and maintenance of these systems in commercial settings.
Most Common Causes of Pilot Light Problems
Thermocouple Failure
Thermocouple failure is the single most common cause of a pilot light that will not stay lit. The thermocouple is a safety device, a metal probe that sits directly in the pilot flame. When the flame heats it, it generates a small millivolt signal that tells the gas valve the pilot is burning. The moment that signal disappears, the valve closes.
Thermocouples wear out over time. Commercial water heaters that run continuous-demand cycles can fail sooner than the manufacturer’s estimated service life. A thermocouple that is simply dirty, bent out of position, or too far from the pilot flame can also generate an inconsistent signal, enough to keep the valve open sometimes, but not reliably.
Signs of thermocouple failure:
- The pilot lights when you hold the button, but goes out the moment you release it
- The pilot stays lit briefly, then dies within 30 to 60 seconds
- The pilot flame looks normal, but the unit still shuts down
Thermocouple replacement is one of the more straightforward commercial gas water heater repairs a qualified technician can perform, and replacement parts are widely available. Browse water heater parts at Wallingford Sales to find compatible components for AO Smith, Rheem, and other major brands.
Gas Supply Issues
Pilot light problems do not always start at the water heater. Sometimes the problem is upstream.
Insufficient gas pressure is a common cause of a pilot that will not stay lit or refuses to light at all. This can happen when multiple gas appliances run simultaneously and draw down pressure at the meter, when a gas regulator starts to fail, or when a supply valve has been partially closed and not fully reopened after maintenance.
For propane-fired units, a low fuel level will produce the same symptoms. This weak or intermittent pilot flame cannot sustain itself even when the thermocouple is functioning correctly.
What to check:
- Confirm the manual shutoff valve on the water heater supply line is fully open
- Check whether other gas appliances in the facility are operating normally
- For propane units, verify the tank level
- If pressure seems low across multiple appliances, contact your gas utility or a licensed plumber to test line pressure at the meter
For more on gas-fired commercial water heater operation and maintenance, the Wallingford Sales blog has a full section on gas-fired water heaters worth bookmarking.
A Dirty or Clogged Pilot Orifice
The pilot orifice is a small brass fitting with a tiny opening that meters gas flow to the pilot flame. Dust, debris, and mineral deposits can partially block that opening over time, producing a weak, unsteady flame that cannot reliably heat the thermocouple.
A weak pilot flame often looks yellow or orange rather than a healthy blue with a small yellow tip. It may flicker under normal air movement in the mechanical room, which would not affect a properly burning pilot.
Cleaning the pilot orifice is a delicate job. The orifice opening is small enough that the wrong cleaning tool could enlarge it, permanently changing the gas flow. This is a job for a licensed gas technician, not a maintenance staff member with a paperclip.
Draft and Airflow Problems
Commercial mechanical rooms are not always well sealed. HVAC changes, exhaust fans, open doors, and seasonal pressure differences can create drafts that repeatedly blow out a standing pilot flame, making it appear like a gas or thermocouple problem when the real issue is airflow.
This is more common in facilities that have undergone recent renovations, had new exhaust equipment installed, or had changes to HVAC zoning. If the pilot goes out repeatedly but relights easily each time, and no other cause is apparent, document when it happens: time of day, weather conditions, and whether nearby exhaust fans were running. Patterns in that data often point directly to the airflow source.
A licensed HVAC or plumbing contractor can perform a combustion air assessment to confirm whether the mechanical room has adequate makeup air for the water heater and other gas appliances.
Faulty Gas Valve
If thermocouple replacement and gas supply checks come back clean and the pilot light problems persist, the gas valve itself may be failing. The gas valve controls the flow of gas to both the pilot and the main burner, and it houses the safety mechanism that responds to the thermocouple’s signal.
Gas valve failure is less common than thermocouple failure but more serious. A valve that sticks, leaks internally, or fails to respond to the thermocouple signal creates both a reliability problem and a potential safety issue. Replacing a gas valve on a commercial unit is a job for a licensed plumber or gas technician. Facility maintenance staff should never attempt this.
If the water heater is older and the gas valve has failed, it is worth running a repair-versus-replace calculation before investing in a new valve. The Wallingford Sales blog on commercial water heater maintenance covers how to think through that decision.
Standing Pilot vs. Intermittent Ignition: Does It Change the Troubleshooting?
Yes, somewhat.
On a standing pilot system, most pilot light problems trace back to the thermocouple, the gas supply, or the pilot orifice. The components covered above.
On an intermittent ignition device (IID) system, the igniter fires electronically each time the burner needs to run. Pilot light problems on these units may involve the igniter itself, the ignition control module, or the wiring between them. IID systems also have a flame sensor (functionally similar to a thermocouple) that can fail, causing the same “lights but won’t stay lit” symptom.
IID systems are more complex to troubleshoot without diagnostic equipment and manufacturer documentation. If your commercial gas water heater uses intermittent ignition and is experiencing repeated ignition failures, a factory-trained technician familiar with that specific control system will get to the answer faster than a generalist.
When to Stop Troubleshooting and Call a Professional
Some pilot light problems are manageable for a knowledgeable facility manager to investigate. Others are not.
Call a licensed plumber or gas technician immediately if:
- You smell gas at any point during troubleshooting
- The pilot will not light at all despite a confirmed gas supply
- The unit has already been through a thermocouple replacement, and the problem continues
- You suspect a gas valve issue
- The unit is making unusual sounds alongside the ignition failure
Natural gas and propane systems carry real risks when handled incorrectly. The National Fire Protection Association (NFPA) publishes NFPA 54, the National Fuel Gas Code, which governs safe installation and service of commercial gas appliances. A licensed professional should handle any repair that goes beyond a visual inspection and basic component swaps.
Get the Parts and Support You Need from Wallingford Sales
When pilot light problems take a commercial water heater offline, fast access to the right parts makes all the difference. Wallingford Sales stocks replacement thermocouples, thermopiles, gas valves, and related components for AO Smith, Rheem, and other major commercial water heater brands. Whether your technician needs a single part or you are evaluating a full unit replacement, our team knows commercial gas systems. It can help you find the right solution without wasting time on the wrong part.
Browse our commercial water heater parts or shop our full line of natural gas and propane water heaters at Wallingford Sales. When downtime is not an option, we are the supplier your technician can count on.
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