Oso
Oso 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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E01
Digital Oso water heater will not heat; display shows E01 and water remains cold.
Primary Heating Element Open Circuit
E02
Oso water heater shows E02 and shuts down shortly after calling for heat.
Overheat / Safety Thermostat Trip
E03
Oso digital water heater displays E03 and does not heat; temperature reading seems incorrect or frozen.
Tank Temperature Sensor (NTC) Fault
E04
Oso water heater shows E04 and stops heating; unit may have recently overheated or been drained.
Dry-Fire / Low Water Level Protection Trip
E05
Oso water heater displays E05 and will not operate; may be associated with a recent power surge or wiring work.
Control PCB Communication / Internal Fault
E06
Oso water heater shows E06; display may be blank or flickering and buttons unresponsive.
User Interface / Display Module Fault
E07
Oso water heater intermittently shuts down with E07; may be associated with very high or low mains voltage.
Supply Voltage Out of Range
E08
Oso water heater shows E08 and does not heat; often occurs on models with external temperature sensors or mixing valves.
Outlet / Secondary Temperature Sensor Fault
E09
Oso water heater with integrated circulation pump shows E09 and stops heating.
Circulation Pump Fault / No Flow Detected
E10
Oso water heater shows E10 and will not start heating; often associated with external control signals.
External Control / BMS Signal Fault
E11
Oso water heater intermittently shows E11; heating stops and restarts after some time.
Sensor Calibration / Temperature Drift Error
E12
Oso water heater shows E12; unit may still heat but with limited performance.
Partial Heating Element Failure / Phase Loss (Multi-element models)
E13
Oso water heater shows E13 and may shut down; often associated with high tank pressure or discharge from safety valve.
Pressure Sensor / High Pressure Fault (where fitted)
E14
Oso water heater shows E14 and refuses to heat; may be linked to safety interlocks.
Safety Interlock Open (Door/Panel/Overheat Chain)
E15
Oso water heater shows E15; unit may not respond to Wi‑Fi or remote app control (on connected models).
Communication Fault with Remote Module
E16
Oso water heater shows E16 and limits output; may be associated with anti‑scald protection.
Thermostatic Mixing Valve / Outlet Overtemperature Fault
E17
Oso water heater shows E17; heating is disabled until the fault clears.
Earth Leakage / Ground Fault Detected
E18
Oso water heater shows E18; may be associated with frequent on/off cycling or unstable readings.
Rapid Temperature Fluctuation / Sensor Noise
E19
Oso water heater shows E19 and may not follow programmed schedules.
Real-Time Clock / Memory Error
E20
Oso water heater shows E20; unit may lock out after repeated faults.
Lockout Due to Repeated Overheat or Sensor Errors
Symptom
Oso water heater causes water hammer or banging noises in pipework when heating or taps are opened/closed.
Hydraulic Shock / Expansion Issues
Symptom
Oso water heater cycles on and off rapidly, with small temperature swings and frequent relay clicks.
Short Cycling / Poor Temperature Differential
Symptom
Oso water heater does not restart heating after hot water is drawn; requires manual reset or power cycle.
Intermittent Thermostat or Control Fault
Symptom
Oso water heater emits a metallic or rusty discoloration in hot water.
Internal Corrosion / Anode Depletion
Symptom
Oso water heater emits a plastic or burning smell during operation.
Overheating Electrical Components
Symptom
Oso water heater installed on an unvented system discharges water from the expansion relief valve (not T&P) frequently.
Expansion Relief Valve Operation
Symptom
Oso water heater leaking from around the immersion heater flange or element boss.
Element Gasket / Flange Seal Leak
Symptom
Oso water heater leaking from the cold inlet combination valve or its connections.
Inlet Control Group Leak
Symptom
Oso water heater making loud popping or kettling noises during heating.
Limescale Buildup on Heating Element and Tank Surfaces
Symptom
Oso water heater not heating at all, no error code displayed; water remains cold.
No Heat / Dead Heating Circuit
Symptom
Oso water heater produces insufficient hot water; runs lukewarm or cool after a short time.
Reduced Heating Capacity / Partial Element Failure
Symptom
Oso water heater produces very low hot water pressure or flow at taps.
Restricted Hot Water Outlet / Flow
Symptom
Oso water heater trips the breaker or RCD when heating is called for.
Electrical Short or Earth Leakage
Symptom
Oso water heater’s casing feels excessively hot to touch during operation.
Insulation Degradation / Overheating
Symptom
Oso water heater’s digital display is blank, but power is present at the unit.
No Display / UI Power Failure
Symptom
Oso water heater’s digital display works, but buttons or touch controls do not respond.
Keypad / Touch Interface Failure
Symptom
Oso water heater’s expansion vessel frequently discharges water or loses charge.
Failed Expansion Vessel Diaphragm
Symptom
Water dripping from the Oso water heater’s temperature and pressure (T&P) relief valve discharge pipe.
Temperature and Pressure Relief Valve Discharge
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Digital Oso water heater will not heat; display shows E01 and water remains cold.
|
Primary Heating Element Open Circuit | View Details |
| E02 |
Oso water heater shows E02 and shuts down shortly after calling for heat.
|
Overheat / Safety Thermostat Trip | View Details |
| E03 |
Oso digital water heater displays E03 and does not heat; temperature reading seems incorrect or frozen.
|
Tank Temperature Sensor (NTC) Fault | View Details |
| E04 |
Oso water heater shows E04 and stops heating; unit may have recently overheated or been drained.
|
Dry-Fire / Low Water Level Protection Trip | View Details |
| E05 |
Oso water heater displays E05 and will not operate; may be associated with a recent power surge or wiring work.
|
Control PCB Communication / Internal Fault | View Details |
| E06 |
Oso water heater shows E06; display may be blank or flickering and buttons unresponsive.
|
User Interface / Display Module Fault | View Details |
| E07 |
Oso water heater intermittently shuts down with E07; may be associated with very high or low mains voltage.
|
Supply Voltage Out of Range | View Details |
| E08 |
Oso water heater shows E08 and does not heat; often occurs on models with external temperature sensors or mixing valves.
|
Outlet / Secondary Temperature Sensor Fault | View Details |
| E09 |
Oso water heater with integrated circulation pump shows E09 and stops heating.
|
Circulation Pump Fault / No Flow Detected | View Details |
| E10 |
Oso water heater shows E10 and will not start heating; often associated with external control signals.
|
External Control / BMS Signal Fault | View Details |
| E11 |
Oso water heater intermittently shows E11; heating stops and restarts after some time.
|
Sensor Calibration / Temperature Drift Error | View Details |
| E12 |
Oso water heater shows E12; unit may still heat but with limited performance.
|
Partial Heating Element Failure / Phase Loss (Multi-element models) | View Details |
| E13 |
Oso water heater shows E13 and may shut down; often associated with high tank pressure or discharge from safety valve.
|
Pressure Sensor / High Pressure Fault (where fitted) | View Details |
| E14 |
Oso water heater shows E14 and refuses to heat; may be linked to safety interlocks.
|
Safety Interlock Open (Door/Panel/Overheat Chain) | View Details |
| E15 |
Oso water heater shows E15; unit may not respond to Wi‑Fi or remote app control (on connected models).
|
Communication Fault with Remote Module | View Details |
| E16 |
Oso water heater shows E16 and limits output; may be associated with anti‑scald protection.
|
Thermostatic Mixing Valve / Outlet Overtemperature Fault | View Details |
| E17 |
Oso water heater shows E17; heating is disabled until the fault clears.
|
Earth Leakage / Ground Fault Detected | View Details |
| E18 |
Oso water heater shows E18; may be associated with frequent on/off cycling or unstable readings.
|
Rapid Temperature Fluctuation / Sensor Noise | View Details |
| E19 |
Oso water heater shows E19 and may not follow programmed schedules.
|
Real-Time Clock / Memory Error | View Details |
| E20 |
Oso water heater shows E20; unit may lock out after repeated faults.
|
Lockout Due to Repeated Overheat or Sensor Errors | View Details |
| – |
Oso water heater causes water hammer or banging noises in pipework when heating or taps are opened/closed.
|
Hydraulic Shock / Expansion Issues | View Details |
| – |
Oso water heater cycles on and off rapidly, with small temperature swings and frequent relay clicks.
|
Short Cycling / Poor Temperature Differential | View Details |
| – |
Oso water heater does not restart heating after hot water is drawn; requires manual reset or power cycle.
|
Intermittent Thermostat or Control Fault | View Details |
| – |
Oso water heater emits a metallic or rusty discoloration in hot water.
|
Internal Corrosion / Anode Depletion | View Details |
| – |
Oso water heater emits a plastic or burning smell during operation.
|
Overheating Electrical Components | View Details |
| – |
Oso water heater installed on an unvented system discharges water from the expansion relief valve (not T&P) frequently.
|
Expansion Relief Valve Operation | View Details |
| – |
Oso water heater leaking from around the immersion heater flange or element boss.
|
Element Gasket / Flange Seal Leak | View Details |
| – |
Oso water heater leaking from the cold inlet combination valve or its connections.
|
Inlet Control Group Leak | View Details |
| – |
Oso water heater making loud popping or kettling noises during heating.
|
Limescale Buildup on Heating Element and Tank Surfaces | View Details |
| – |
Oso water heater not heating at all, no error code displayed; water remains cold.
|
No Heat / Dead Heating Circuit | View Details |
| – |
Oso water heater produces insufficient hot water; runs lukewarm or cool after a short time.
|
Reduced Heating Capacity / Partial Element Failure | View Details |
| – |
Oso water heater produces very low hot water pressure or flow at taps.
|
Restricted Hot Water Outlet / Flow | View Details |
| – |
Oso water heater trips the breaker or RCD when heating is called for.
|
Electrical Short or Earth Leakage | View Details |
| – |
Oso water heater’s casing feels excessively hot to touch during operation.
|
Insulation Degradation / Overheating | View Details |
| – |
Oso water heater’s digital display is blank, but power is present at the unit.
|
No Display / UI Power Failure | View Details |
| – |
Oso water heater’s digital display works, but buttons or touch controls do not respond.
|
Keypad / Touch Interface Failure | View Details |
| – |
Oso water heater’s expansion vessel frequently discharges water or loses charge.
|
Failed Expansion Vessel Diaphragm | View Details |
| – |
Water dripping from the Oso water heater’s temperature and pressure (T&P) relief valve discharge pipe.
|
Temperature and Pressure Relief Valve Discharge | View Details |
No matching codes found
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