Hayward H-Series HF Error Code: False Flame Detection Troubleshooting

Understanding the HF Code

The HF (Hot Flame or False Flame) error code is triggered when the control board detects a flame signal at inappropriate times - either before ignition is commanded or after the gas valve should be closed. This is a critical safety feature designed to prevent uncontrolled gas combustion.

The flame detection system uses a flame rectification circuit where the flame acts as a diode, converting AC voltage to DC microamps. When the control board sees this DC signal without commanding gas flow, it triggers the HF code and locks out operation.

How Flame Detection Works

The flame sensing circuit consists of:

• Flame sensor rod: Stainless steel probe positioned in flame path
• Ground reference: Burner assembly acts as ground
• AC voltage source: Control board applies ~120V AC to sensor
• Rectification circuit: Flame creates DC current path to ground
• Microamp detection: Board measures DC current (2-10 μA normal)

Common Causes of HF Codes

Electrical Issues (Most Common - 70%)

• Shorted flame sensor: Sensor shorting to ground
• Moisture in connections: Creating false conductivity
• Damaged sensor wire: Insulation failure causing shorts
• Control board failure: False readings from damaged circuit
• Electrical interference: EMF from nearby equipment

Mechanical Issues (Less Common - 25%)

• Stuck gas valve: Valve not fully closing (DANGEROUS)
• Flame rollout: Flame reaching sensor when it shouldn't
• Delayed flame extinction: Flame persisting after shutdown
• Carbon buildup: Creating conductive path on sensor

Environmental Factors (Rare - 5%)

• High humidity: Moisture creating false signals
• Salt air corrosion: Coastal environments affecting connections
• Lightning damage: Surge damage to sensing circuit

Immediate Safety Checks

Step 1: Verify No Actual Flame

1. Turn off heater at control panel
2. Wait 5 minutes for any flame to extinguish
3. Look through sight glass (if equipped)
4. Listen for combustion sounds
5. Check for heat at exhaust vent
6. Smell for gas odor

If flame is present or gas odor detected:

• Shut off gas supply immediately
• Turn off power at breaker
• Call professional service
• Do not attempt DIY repair

Step 2: Check Error Timing

• Note when HF appears:
  • Immediately on power-up = likely electrical issue
  • During pre-purge = sensor or wiring problem
  • After shutdown = possible stuck valve or flame persistence

Detailed Troubleshooting

Basic Diagnostics (Power Off)

1. Visual Inspection

• Check flame sensor for visible damage
• Look for cracked ceramic insulator
• Inspect wire for cuts or burn marks
• Check for moisture in electrical compartment
• Look for carbon tracking on components

2. Sensor Isolation Test

1. Turn off power and gas
2. Disconnect flame sensor wire at control board
3. Power on heater (gas remains off)
4. If HF clears, problem is sensor or wiring
5. If HF remains, problem is control board

Advanced Testing (Technician Level)

3. Flame Sensor Insulation Test

1. Remove flame sensor from burner assembly
2. Clean sensor rod with steel wool
3. Test resistance from rod to sensor body
4. Should show open circuit (infinite ohms)
5. Any continuity indicates damaged insulator

4. Sensor Wire Testing

1. Disconnect sensor wire at both ends
2. Test insulation resistance to ground
3. Should be >1 megohm
4. Check for pinched or damaged sections
5. Replace if insulation compromised

5. Control Board Diagnostics

1. With sensor disconnected
2. Measure AC voltage at sensor terminal
3. Should see ~120V AC during operation
4. Check for DC offset (should be <1V DC)
5. High DC indicates board problem

6. Gas Valve Verification

1. With system off, check valve physically
2. Valve should be fully closed (no gas flow)
3. Listen for gas flow with valve de-energized
4. If gas passing, valve needs immediate replacement

Component Testing Procedures

Flame Sensor Microamp Test

1. With heater running normally (if possible)
2. Disconnect sensor wire from board
3. Set meter to DC microamps
4. Connect meter in series with sensor circuit
5. Normal reading: 2-10 microamps
6. No flame should show 0 microamps

Ground Reference Check

1. Verify good ground at burner assembly
2. Check ground wire connections
3. Test continuity from burner to chassis ground
4. Resistance should be <1 ohm
5. Poor ground can cause false signals

Moisture Detection

• Check all connections for corrosion
• Look for water tracks on circuit board
• Test with moisture meter if available
• Dry components with compressed air
• Apply dielectric grease to connections

Solutions by Cause

For Electrical Issues

• Shorted sensor: Replace flame sensor assembly
• Damaged wire: Replace or repair sensor wire
• Moisture: Dry components, seal enclosure
• Board failure: Replace control board
• Poor ground: Clean and tighten ground connections

For Mechanical Issues

• Stuck gas valve: Replace valve immediately (PRIORITY)
• Carbon buildup: Clean sensor with fine steel wool
• Flame rollout: Check heat exchanger and venting
• Delayed extinction: Verify proper gas pressure

For Environmental Issues

• High humidity: Improve ventilation, add desiccant
• Corrosion: Clean connections, apply protective coating
• Surge damage: Install surge protector, replace damaged components

Replacement Parts

• Flame Sensor Rod: HADXFLS1930
• Sensor Wire Assembly: HADXFLW1930
• Gas Valve: HADXGSV1930 (Natural) or HADXGSV19301 (Propane)
• Control Board: Model-specific part number
• Sensor Mounting Gasket: HADXGKT1930

Prevention Measures

• Annual flame sensor cleaning
• Keep electrical compartment dry and sealed
• Check and tighten connections yearly
• Install surge protection
• Maintain proper combustion (prevents carbon buildup)
• Regular gas valve operation checks
• Apply dielectric grease to outdoor connections

Special Considerations

Intermittent HF Codes

If HF appears randomly:

• Usually indicates marginal electrical connection
• Check for vibration-induced shorts
• Look for temperature-related expansion/contraction
• Monitor during different weather conditions

HF After Service

If HF appears after maintenance:

• Verify sensor properly positioned in flame
• Check that sensor wire routing avoids hot surfaces
• Ensure good ground connection restored
• Confirm no moisture introduced during service

Multiple Error Codes

HF accompanied by other codes may indicate:

• Control board failure affecting multiple circuits
• Power quality issues
• Lightning or surge damage
• Systematic grounding problem

When to Call a Professional

Immediately call for service if:

• Gas odor detected at any time
• Visible flame when heater should be off
• HF code returns after sensor replacement
• Multiple components test bad
• You're not comfortable with gas appliance repair

← Back to Universal H-Series Troubleshooting Guide