Bradford White Water Heater Error Code 5 — Flame Sense Circuit Fault

Bradford White gas water heaters with the Icon System control flash error code 5 (five slow flashes) when the flame sense circuit detects a problem. The burner lit successfully, but the control lost the flame-proving signal or never received it.

This is different from error code 4 (ignition lockout) — the burner actually fired, but the control can’t confirm the flame is present. It shuts the gas valve as a safety precaution.

Jump to Fix

• What Error Code 5 Means
• Quick Reference Table
• Most Common Causes
• Step-by-Step Diagnosis
• Parts and Costs
• When to Call a Tech

What Error Code 5 Means

The flame sense circuit uses a metal rod (the flame sensor) and a small electrical current through the flame to prove combustion is happening. When the burner is lit, flame ions conduct a tiny DC current — typically 2-10 microamps — from the sensor rod to ground. The gas control monitors this current. If it drops below the minimum threshold during operation, the control assumes the flame went out and closes the gas valve.

Models affected: Bradford White gas water heaters with electronic ignition — Defender Safety System (DSI) and power-vent models. Not applicable to standing pilot models.

The burner may have been burning normally for minutes or hours before the error triggers. The heater stops producing hot water immediately when the code appears.

Quick Reference Table

Most Common Causes

The flame sensor rod is exposed to combustion byproducts every time the burner runs. Over time, a thin layer of carbon and oxidation builds up on the rod surface, insulating it and blocking the microamp flame signal. Cleaning it is the fix about 80% of the time.

Step-by-Step Diagnosis

Step 1: Confirm the error code

Turn the gas control knob to OFF, wait 30 seconds, and turn it back to your temperature setting. If the burner lights but error code 5 returns within a few minutes, the flame sense circuit is the issue.

A burner that runs for a cycle or two before error code 5 appears points to an intermittent sensor issue — the signal degrades as the sensor heats up and oxidation reduces conductivity.

Step 2: Clean the flame sensor

This is the most effective fix and takes about 10 minutes.

1. Turn the gas control knob to OFF and wait 5 minutes
2. Shut off the gas supply at the manual shutoff valve
3. Remove the burner access panel at the tank bottom
4. Locate the flame sensor — a metal rod approximately 1/8” thick, mounted on or near the burner assembly
5. Remove the mounting screw and pull the sensor straight out
6. Clean the metal rod thoroughly with fine emery cloth or 220-grit sandpaper — don’t use steel wool (it leaves metallic particles that cause tracking)
7. Wipe with a dry, lint-free cloth
8. Reinstall and test the heater

A properly cleaned flame sensor should have a bright, even metallic surface with no dark spots or carbon residue.

Step 3: Check the sensor position

The flame sensor must be positioned so the burner flame directly contacts the rod. If the bracket is bent or the sensor wasn’t fully seated after cleaning, the signal will be weak.

• The sensor rod should extend into the flame cone, not just the outer envelope
• The gap between the sensor tip and the burner surface is usually 1/4” to 3/8”
• If the burner flame is yellow or lazy instead of blue, the burner or flue may need cleaning first

Step 4: Check the sensor wiring and ground

The flame sensor relies on a good ground path through the tank body and gas piping. A weak ground drops the microamp signal.

1. Check the ground wire connecting the tank to the gas piping or electrical panel — it must be clean and tight
2. Inspect the sensor wire from the rod to the gas valve connector — look for cracked insulation, corrosion, or loose terminals
3. Check the ceramic insulator at the base of the sensor rod — carbon tracking across the insulator creates a ground path that bypasses the flame

If the ceramic insulator has black carbon tracks, replace the sensor — cleaning won’t fix the tracking.

Step 5: Measure the flame signal (advanced)

If you have a microamp meter (standard multimeter with a microamp setting):

1. Connect the meter in series with the flame sensor wire — disconnect the sensor lead from the gas valve and connect the meter between the valve terminal and the sensor wire
2. Set the meter to DC microamps (μA)
3. Start the heater — the burner should light
4. Read the signal:
   • 4-10 μA: Normal — flame signal is adequate
   • 1-3 μA: Marginal — sensor needs cleaning or repositioning
   • Under 1 μA: No flame sense — sensor is dirty, failed, or not in the flame

A reading under 1 μA with a visually clean sensor in the flame path points to a gas control valve circuit failure.

Step 6: Test with the burner cover off

A trick for intermittent error code 5: run the heater with the burner access panel removed. If the code doesn’t appear with the panel off, the issue is air supply or flue gas recirculation, not the sensor itself.

• With the panel off, the burner receives more combustion air and the flame is more stable
• If the code only appears with the panel installed, check the flue for partial blockage or the air intake for restrictions

Parts and Costs

When to Call a Tech

Call a licensed technician if:

• You cleaned the flame sensor multiple times and error code 5 still returns within days
• The ceramic insulator shows carbon tracking — the sensor can’t be recovered
• Your multimeter shows a weak flame signal (under 2 μA) with a clean, properly positioned sensor
• The error triggers immediately on startup and you’ve checked all wiring and connections
• You’re not comfortable working near gas components

Average repair cost with a technician: $120–$250 for flame sensor replacement including diagnosis. Gas control valve replacement: $300–$600.

Related Guides

• Bradford White Water Heater Error Code 4 — Ignition Lockout Fix
• Bradford White Water Heater Error Code 2 — Temperature Sensor Fault Fix
• Bradford White Water Heater Error Code 8 — Blower/Inducer Problem

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