Protherm
Protherm Water Heaters Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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F0
Water heater does not start heating; the display shows F0 shortly after power-up.
Internal Control Board Configuration / Parameter Error
F1
The display shows F1, and the burner does not ignite; no hot water is produced.
Flow Sensor / Turbine Fault
F10
F10 error, appliance does not start, may appear after power disturbances.
Low Voltage / Power Supply Fault
F11
F11 displayed, appliance may start and stop erratically, communication-related issues.
Internal Communication Error (PCB / Display / Module Bus)
F12
F12 error, appliance does not respond correctly to temperature settings.
User Interface / Keypad Fault
F13
F13 displayed, appliance may run at reduced power or shut down.
Gas Valve Modulation / Control Fault
F14
F14 error, appliance does not start, may be associated with fan speed control issues.
Fan Speed / Tachometer Fault
F15
F15 displayed; appliance may not detect water flow correctly or modulate temperature.
Flow Sensor Signal Range / Plausibility Error
F2
The unit locks out with F2; the burner shuts down shortly after ignition or during operation.
Flame Detection / Ionization Fault
F20
F20 error; appliance shuts down with overheat indication; may occur during long draws of hot water.
Primary Circuit Overheat / Circulation Fault
F22
F22 displayed; appliance does not start; may indicate dry operation or low water content.
Low Water Content / Dry-Fire Protection
F23
F23 error; appliance stops; temperature difference between flow and return is excessive.
Flow/Return Temperature Differential Fault
F24
F24 displayed; appliance may start then quickly shut down; temperatures rise too fast.
Rapid Temperature Rise / Pump Protection
F25
F25 error; appliance locks out; may be associated with flue gas recirculation or high flue temperature.
Flue Gas Recirculation / Overtemperature
F26
F26 displayed; appliance may not modulate correctly or may shut down.
Gas Valve Control / Internal Error
F27
F27 error; appliance detects flame when there should be none or vice versa.
Flame Detection / False Flame Signal
F28
F28 displayed; ignition attempts fail; no flame established.
Ignition Lockout (No Flame Detected)
F29
F29 error; flame is established then lost during operation.
Flame Loss During Operation
F3
F3 is displayed; the burner does not start or shuts down, and the fan may run briefly.
Flue Gas Temperature Sensor Fault / Overheat
F32
F32 displayed; fan speed or airflow readings are implausible.
Fan Speed Sensor / Airflow Plausibility Fault
F36
F36 error: appliance detects flue gas recirculation or blocked flue conditions.
Flue Gas Safety / Blocked Flue Detection
F4
F4 error; the burner does not ignite, and you may hear clicking but no flame.
Ignition Failure
F41
F41 displayed; appliance may not regulate power correctly.
Flow Temperature Sensor / Control Deviation
F42
F42 error: return temperature sensor readings are implausible.
Return Temperature Sensor Fault
F49
F49 displayed; control electronics detect low supply voltage or a communication error.
Low Voltage / Bus Communication Fault
F5
F5 displayed, appliance attempts to start but shuts down; fan may not run correctly.
Fan / Air Pressure Switch Fault
F6
F6 error, water heater stops, temperature readings on the display are unrealistic or fluctuating.
DHW Temperature Sensor (NTC) Fault
F61
F61 error: gas valve control fault detected; appliance locks out.
Gas Valve Relay / Drive Fault
F62
F62 displayed; gas valve relay timing or de-energization fault.
Gas Valve Shutoff Timing Fault
F7
F7 displayed, heater does not start or shuts down, flow temperature reading is incorrect.
Primary Flow Temperature Sensor Fault
F70
F70 error: display and main PCB configuration mismatch.
Configuration / Coding Plug Error
F73
F73 displayed; water pressure sensor signal too low or missing.
Water Pressure Sensor Fault (Low Signal)
F74
F74 error: water pressure sensor signal too high or out of range.
Water Pressure Sensor Fault (High Signal)
F8
F8 error, appliance overheats and shuts down, casing may feel very hot.
Safety Overheat Thermostat Tripped
F83
F83 displayed; abnormal temperature rise at start-up.
Start-Up Temperature Rise Fault
F84
F84 error; flow and return temperature sensors show an implausible difference at start-up.
Flow/Return Sensor Correlation Fault
F85
F85 displayed; flow and return sensors show identical values when they should differ.
Flow/Return Sensor Short or Swap Fault
F9
F9 displayed, appliance locks out, may be associated with very high temperature readings.
Overtemperature Lockout / Sensor Plausibility Error
Symptom
Water heater cycles on and off rapidly with small hot water draws
Short Cycling on Low Flow
Symptom
Water heater does not start at all; no display or lights.
No Power / Dead Appliance
Symptom
Water heater emits a whistling or high-pitched noise during operation.
Flow-Induced or Combustion Noise
Symptom
Water heater gives off a burning smell or signs of overheating plastic
Overheating Electrical or Plastic Components
Symptom
Water heater has power but produces no hot water at any tap.
No Heating / No DHW Production
Symptom
Water heater leaks water from the bottom of the casing.
Internal Water Leak
Symptom
Water heater makes loud banging or knocking noises when heating.
Kettling / Boiling in Heat Exchanger
Symptom
Water heater pilot (on older Protherm models) will not stay lit
Pilot Flame Holding Fault
Symptom
Water heater produces hot water but flow rate is very low
Reduced DHW Flow
Symptom
Water heater produces hot water but the temperature is too low.
Insufficient Outlet Temperature
Symptom
Water heater runs but hot water smells metallic or rusty
Corrosion / Contaminated Water
Symptom
Water heater temperature fluctuates, alternating between hot and cold during a shower.
Temperature Instability / Cycling
Symptom
Water heater trips the household RCD / GFCI when it starts
Earth Leakage / Insulation Fault
Symptom
Water heater vibrates excessively or rattles when running
Mechanical Vibration / Mounting Fault
Symptom
Water heater's safety valve or relief valve is dripping water regularly
Overpressure / Expansion Relief Discharge
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F0 |
Water heater does not start heating; the display shows F0 shortly after power-up.
|
Internal Control Board Configuration / Parameter Error | View Details |
| F1 |
The display shows F1, and the burner does not ignite; no hot water is produced.
|
Flow Sensor / Turbine Fault | View Details |
| F10 |
F10 error, appliance does not start, may appear after power disturbances.
|
Low Voltage / Power Supply Fault | View Details |
| F11 |
F11 displayed, appliance may start and stop erratically, communication-related issues.
|
Internal Communication Error (PCB / Display / Module Bus) | View Details |
| F12 |
F12 error, appliance does not respond correctly to temperature settings.
|
User Interface / Keypad Fault | View Details |
| F13 |
F13 displayed, appliance may run at reduced power or shut down.
|
Gas Valve Modulation / Control Fault | View Details |
| F14 |
F14 error, appliance does not start, may be associated with fan speed control issues.
|
Fan Speed / Tachometer Fault | View Details |
| F15 |
F15 displayed; appliance may not detect water flow correctly or modulate temperature.
|
Flow Sensor Signal Range / Plausibility Error | View Details |
| F2 |
The unit locks out with F2; the burner shuts down shortly after ignition or during operation.
|
Flame Detection / Ionization Fault | View Details |
| F20 |
F20 error; appliance shuts down with overheat indication; may occur during long draws of hot water.
|
Primary Circuit Overheat / Circulation Fault | View Details |
| F22 |
F22 displayed; appliance does not start; may indicate dry operation or low water content.
|
Low Water Content / Dry-Fire Protection | View Details |
| F23 |
F23 error; appliance stops; temperature difference between flow and return is excessive.
|
Flow/Return Temperature Differential Fault | View Details |
| F24 |
F24 displayed; appliance may start then quickly shut down; temperatures rise too fast.
|
Rapid Temperature Rise / Pump Protection | View Details |
| F25 |
F25 error; appliance locks out; may be associated with flue gas recirculation or high flue temperature.
|
Flue Gas Recirculation / Overtemperature | View Details |
| F26 |
F26 displayed; appliance may not modulate correctly or may shut down.
|
Gas Valve Control / Internal Error | View Details |
| F27 |
F27 error; appliance detects flame when there should be none or vice versa.
|
Flame Detection / False Flame Signal | View Details |
| F28 |
F28 displayed; ignition attempts fail; no flame established.
|
Ignition Lockout (No Flame Detected) | View Details |
| F29 |
F29 error; flame is established then lost during operation.
|
Flame Loss During Operation | View Details |
| F3 |
F3 is displayed; the burner does not start or shuts down, and the fan may run briefly.
|
Flue Gas Temperature Sensor Fault / Overheat | View Details |
| F32 |
F32 displayed; fan speed or airflow readings are implausible.
|
Fan Speed Sensor / Airflow Plausibility Fault | View Details |
| F36 |
F36 error: appliance detects flue gas recirculation or blocked flue conditions.
|
Flue Gas Safety / Blocked Flue Detection | View Details |
| F4 |
F4 error; the burner does not ignite, and you may hear clicking but no flame.
|
Ignition Failure | View Details |
| F41 |
F41 displayed; appliance may not regulate power correctly.
|
Flow Temperature Sensor / Control Deviation | View Details |
| F42 |
F42 error: return temperature sensor readings are implausible.
|
Return Temperature Sensor Fault | View Details |
| F49 |
F49 displayed; control electronics detect low supply voltage or a communication error.
|
Low Voltage / Bus Communication Fault | View Details |
| F5 |
F5 displayed, appliance attempts to start but shuts down; fan may not run correctly.
|
Fan / Air Pressure Switch Fault | View Details |
| F6 |
F6 error, water heater stops, temperature readings on the display are unrealistic or fluctuating.
|
DHW Temperature Sensor (NTC) Fault | View Details |
| F61 |
F61 error: gas valve control fault detected; appliance locks out.
|
Gas Valve Relay / Drive Fault | View Details |
| F62 |
F62 displayed; gas valve relay timing or de-energization fault.
|
Gas Valve Shutoff Timing Fault | View Details |
| F7 |
F7 displayed, heater does not start or shuts down, flow temperature reading is incorrect.
|
Primary Flow Temperature Sensor Fault | View Details |
| F70 |
F70 error: display and main PCB configuration mismatch.
|
Configuration / Coding Plug Error | View Details |
| F73 |
F73 displayed; water pressure sensor signal too low or missing.
|
Water Pressure Sensor Fault (Low Signal) | View Details |
| F74 |
F74 error: water pressure sensor signal too high or out of range.
|
Water Pressure Sensor Fault (High Signal) | View Details |
| F8 |
F8 error, appliance overheats and shuts down, casing may feel very hot.
|
Safety Overheat Thermostat Tripped | View Details |
| F83 |
F83 displayed; abnormal temperature rise at start-up.
|
Start-Up Temperature Rise Fault | View Details |
| F84 |
F84 error; flow and return temperature sensors show an implausible difference at start-up.
|
Flow/Return Sensor Correlation Fault | View Details |
| F85 |
F85 displayed; flow and return sensors show identical values when they should differ.
|
Flow/Return Sensor Short or Swap Fault | View Details |
| F9 |
F9 displayed, appliance locks out, may be associated with very high temperature readings.
|
Overtemperature Lockout / Sensor Plausibility Error | View Details |
| – |
Water heater cycles on and off rapidly with small hot water draws
|
Short Cycling on Low Flow | View Details |
| – |
Water heater does not start at all; no display or lights.
|
No Power / Dead Appliance | View Details |
| – |
Water heater emits a whistling or high-pitched noise during operation.
|
Flow-Induced or Combustion Noise | View Details |
| – |
Water heater gives off a burning smell or signs of overheating plastic
|
Overheating Electrical or Plastic Components | View Details |
| – |
Water heater has power but produces no hot water at any tap.
|
No Heating / No DHW Production | View Details |
| – |
Water heater leaks water from the bottom of the casing.
|
Internal Water Leak | View Details |
| – |
Water heater makes loud banging or knocking noises when heating.
|
Kettling / Boiling in Heat Exchanger | View Details |
| – |
Water heater pilot (on older Protherm models) will not stay lit
|
Pilot Flame Holding Fault | View Details |
| – |
Water heater produces hot water but flow rate is very low
|
Reduced DHW Flow | View Details |
| – |
Water heater produces hot water but the temperature is too low.
|
Insufficient Outlet Temperature | View Details |
| – |
Water heater runs but hot water smells metallic or rusty
|
Corrosion / Contaminated Water | View Details |
| – |
Water heater temperature fluctuates, alternating between hot and cold during a shower.
|
Temperature Instability / Cycling | View Details |
| – |
Water heater trips the household RCD / GFCI when it starts
|
Earth Leakage / Insulation Fault | View Details |
| – |
Water heater vibrates excessively or rattles when running
|
Mechanical Vibration / Mounting Fault | View Details |
| – |
Water heater's safety valve or relief valve is dripping water regularly
|
Overpressure / Expansion Relief Discharge | View Details |
No matching codes found
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