Bradford White Ultra Low NOx D series gas error code 81 flash
Flammable vapour sensor out of specification
Quick answer
On Bradford White Ultra Low NOx D series gas, 81 flash is a fault. It means flammable vapour sensor out of specification. A first thing to check: Flammable vapour sensor out of specification.
- Applies to
- Bradford White Ultra Low NOx D series gas
- Bradford White Ultra Low NOx residential D series gas codes · Water Heater
- Type of code
- Fault
- Urgency: Needs attention soon
- First safe check
- Look for a source of moisture near the unit, including a leaking pipe, a dripping vent collar, or a humid crawl space.
What 81 flash means on this model
The vapour sensor is not reporting a believable result, which is a different problem from a real vapour trip. A trip means something about the room, and this means something about the sensor, usually moisture, age, or damaged wiring.
Symptoms you will notice
- Eight-one flashes, then a three second pause
- Code appears with no unusual smell or activity nearby
- Code returns after being cleared, sometimes immediately
- Unit will run but keeps dropping out
- Problem started after a humid spell or after a flood or leak nearby
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- Flammable vapour sensor out of specification
- Moisture on or in the sensor
- Sensor at the end of its service life
- Damage to the sensor wiring
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Look for a source of moisture near the unit, including a leaking pipe, a dripping vent collar, or a humid crawl space.
- Note whether the code follows a flood, a roof leak, or a period of unusual humidity.
- Check the sensor wiring connector for corrosion or a pin that has backed out.
- Confirm whether the appliance is in a location where the sensor sees temperature or moisture swings it was not designed for.
Do not do these
- ×Do not clean the sensor with solvent or spray it with anything. The sensor is a calibrated element.
- ×Do not repeatedly reset and use the unit expecting a different result, because an out of specification sensor will not come back on its own.
- ×Do not substitute a generic sensor for the specified part.
When to call a technician
Book a technician, do not keep resetting it
This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.
- This is a fuel-burning appliance, so treat anything involving a burner, gas valve or flue as technician work. If you smell gas at any point, leave the property and call the gas utility from outside rather than continuing to diagnose.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
A technician job. This is a safety sensor, and the test procedure is part of the service rather than a guess.
What it costs to fix
Parts
Flammable vapour sensor $80 to $200, or gas control $150 to $350 if the sensor is not serviceable separately.
Labor
One to two hours to test and replace.
DIY or technician
A technician job. This is a safety sensor, and the test procedure is part of the service rather than a guess.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Bradford White Ultra Low NOx residential D series gas codes
- Models in scope
- Bradford White Ultra Low NOx D series gas
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.