Weak pilot signalBradford White · Ultra Low NOx D series gas · Water Heater

Bradford White Ultra Low NOx D series gas error code Weak pilot signal

Weak pilot signal on the last call for heat

Book a technician

Also written as short flash once per second, pilot signal

Quick answer

On Bradford White Ultra Low NOx D series gas, Weak pilot signal is a fault. It means weak pilot signal on the last call for heat. A first thing to check: Unstable pilot that is not being held steady by the thermocouple.

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: Book a technician
First safe check: Look at the pilot flame through the sight glass and describe its size and colour. A pilot that is barely lighting the main burner is not a healthy pilot.

Checked 2026-09-26

What Weak pilot signal means on this model

The control is not getting a steady enough reading from the pilot flame to trust it, and it flags the last call for heat. It is the early warning for a pilot that is about to drop out, and it is worth acting on now rather than when there is no hot water.

Symptoms you will notice

A short flash about once a second on the green LED
Hot water runs out more slowly than it should
Unit takes longer to recover between uses
Pilot is visible but small or wavering
Water goes cold while the unit is not being used at all

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:

Unstable pilot that is not being held steady by the thermocouple
Pilot tube blocked or restricted
Oxidation built up on the pilot electrode
Wire damage to the pilot assembly or a poor connection at the gas control

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 at the pilot flame through the sight glass and describe its size and colour. A pilot that is barely lighting the main burner is not a healthy pilot.
Confirm the pilot flame is fully engulfing the flame sensor electrode, which is what the control actually measures.
With the power off at the breaker, unplug the pilot assembly harness from the gas control and look for green corrosion or a loose pin.
Note whether the problem appears on a cold morning only, which points at the thermocouple rather than the gas pressure.

Do not do these

×Do not file or sand the pilot electrode. The control needs a consistent surface to measure against.
×Do not adjust the gas control calibration to compensate for a weak signal. That hides a failing thermocouple and the next failure will be a lockout.
×Do not leave a pilot that keeps dropping out running, because every drop and relight is a warm start that is harder on the burner than a steady flame.

When to call a technician

Worth scheduling, and worth your own checks first

You can usually keep living with this for a short while, but it will not fix itself. Do the safe checks below first, because a tripped switch or a blocked airflow is a five-minute fix that would otherwise cost you a service call.

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.

Looking at the pilot flame through the sight glass is a homeowner task. Anything inside the burner compartment, and any gas piping work, is a licensed technician job.

What it costs to fix

Parts

Thermocouple $25 to $70. Pilot assembly $60 to $180. Pilot tube $20 to $60.

Labor

One to two hours to inspect, clean, and replace the pilot assembly or thermocouple.

DIY or technician