Danfoss
Danfoss Smart Thermostats Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E1
Thermostat display shows E1 and heating does not start or stops shortly after calling for heat.
Room Temperature Sensor Fault (Open Circuit)
E10
Thermostat shows E10 and indicates internal hardware error; most functions are disabled.
Internal Hardware Self-Test Failure
E11
Thermostat shows E11 and cannot detect external temperature or weather compensation input.
Outdoor Sensor Fault
E12
Thermostat shows E12 and fails to control one or more underfloor heating zones via the wiring centre.
Zone Module / Wiring Centre Communication Error
E13
Thermostat shows E13 and indicates internal clock or schedule error; timed programs may not run correctly.
Real-Time Clock / Backup Power Failure
E14
Thermostat shows E14 and refuses to operate due to detected internal temperature sensor overheat.
Internal Thermostat Overheat
E15
Thermostat shows E15 and indicates valve or actuator error; the connected zone does not heat correctly.
Thermal Actuator / Valve Drive Fault
E16
Thermostat shows E16 and indicates pump or boiler control error; heating system does not start.
Boiler / Pump Control Output Fault
E17
Thermostat shows E17 and indicates sensor configuration error; system may not respect floor limits or room control mode.
Sensor Configuration / Type Mismatch
E18
Thermostat shows E18 and indicates firmware update failure; device may be partially functional.
Firmware Update Error
E19
Thermostat shows E19 and indicates internal memory or configuration storage error.
Non-Volatile Memory Fault
E2
Thermostat shows E2 and room temperature reading is clearly wrong (e.g., shows -20°C or 99°C) or fluctuates rapidly.
Room Temperature Sensor Short Circuit
E20
Thermostat shows E20 and indicates bus power or communication overload on multi-zone systems.
Bus Overload / Short Circuit
E3
Thermostat displays E3 and underfloor heating or floor protection functions are disabled.
Floor Sensor Fault (Open Circuit)
E4
Thermostat shows E4 and floor temperature reading is extremely high or low and unstable.
Floor Sensor Short Circuit
E5
Thermostat displays E5 and cannot control the heating actuator or boiler relay.
Output Relay / Triac Fault
E6
Thermostat shows E6 and cannot detect or control the wireless receiver or wiring centre.
Wireless Communication Failure (Thermostat to Receiver)
E7
Thermostat shows E7 and cannot connect to the Danfoss cloud or mobile app; local control may still work.
Wi‑Fi / Internet Connectivity Error
E8
Thermostat shows E8 and the display may dim or reboot intermittently, especially when calling for heat.
Low Supply Voltage / Power Supply Fault
E9
Thermostat shows E9 and refuses to operate heating due to detected over-temperature condition.
Over-Temperature Protection Triggered
Symptom
Some rooms controlled by Danfoss smart thermostats are consistently too cold while others are comfortable.
Zone Imbalance / Incorrect Balancing
Symptom
Thermostat backlight or display flickers or dims randomly while powered.
Unstable Display Power / Backlight Fault
Symptom
Thermostat buttons or touchscreen are unresponsive or register incorrect presses.
User Interface / Keypad Failure
Symptom
Thermostat calls for heat (heat icon on), but radiators or underfloor heating remain cold.
Heat Demand Not Reaching Boiler or Actuators
Symptom
Thermostat cannot be discovered or paired with the Danfoss mobile app during setup.
App Pairing / Commissioning Failure
Symptom
Thermostat display is completely blank and unresponsive; heating does not operate.
No Power to Thermostat
Symptom
Thermostat emits a constant or intermittent clicking or buzzing noise during operation.
Noisy Relay or Power Electronics
Symptom
Thermostat frequently cycles the boiler or actuators on and off in short intervals (short cycling).
Short Cycling of Heating System
Symptom
Thermostat frequently shows low battery warnings (for battery-powered Danfoss smart thermostats or wireless sensors).
Excessive Battery Drain
Symptom
Thermostat intermittently disconnects from the Danfoss cloud or app, showing offline status.
Intermittent Cloud Connectivity
Symptom
Thermostat loses time, date, or schedule settings after every power cut.
Loss of Time and Schedule After Power Interruption
Symptom
Thermostat or wiring centre has a noticeable burning smell or visible scorch marks.
Overheating / Electrical Damage
Symptom
Thermostat or wiring centre makes a loud pop and stops working after a lightning storm or power surge.
Surge Damage to Electronics
Symptom
Thermostat overshoots the set temperature by several degrees before turning the heating off.
Temperature Overshoot / Poor Control Tuning
Symptom
Thermostat powers on but does not call for heat even when room temperature is well below setpoint.
No Heat Demand from Thermostat
Symptom
Thermostat shows room temperature that is clearly inaccurate compared to other thermometers.
Inaccurate Room Temperature Measurement
Symptom
Underfloor heating controlled by the thermostat causes floor to feel excessively hot or damages floor covering.
Floor Overheating in Underfloor Heating System
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E1 |
Thermostat display shows E1 and heating does not start or stops shortly after calling for heat.
|
Room Temperature Sensor Fault (Open Circuit) | View Details |
| E10 |
Thermostat shows E10 and indicates internal hardware error; most functions are disabled.
|
Internal Hardware Self-Test Failure | View Details |
| E11 |
Thermostat shows E11 and cannot detect external temperature or weather compensation input.
|
Outdoor Sensor Fault | View Details |
| E12 |
Thermostat shows E12 and fails to control one or more underfloor heating zones via the wiring centre.
|
Zone Module / Wiring Centre Communication Error | View Details |
| E13 |
Thermostat shows E13 and indicates internal clock or schedule error; timed programs may not run correctly.
|
Real-Time Clock / Backup Power Failure | View Details |
| E14 |
Thermostat shows E14 and refuses to operate due to detected internal temperature sensor overheat.
|
Internal Thermostat Overheat | View Details |
| E15 |
Thermostat shows E15 and indicates valve or actuator error; the connected zone does not heat correctly.
|
Thermal Actuator / Valve Drive Fault | View Details |
| E16 |
Thermostat shows E16 and indicates pump or boiler control error; heating system does not start.
|
Boiler / Pump Control Output Fault | View Details |
| E17 |
Thermostat shows E17 and indicates sensor configuration error; system may not respect floor limits or room control mode.
|
Sensor Configuration / Type Mismatch | View Details |
| E18 |
Thermostat shows E18 and indicates firmware update failure; device may be partially functional.
|
Firmware Update Error | View Details |
| E19 |
Thermostat shows E19 and indicates internal memory or configuration storage error.
|
Non-Volatile Memory Fault | View Details |
| E2 |
Thermostat shows E2 and room temperature reading is clearly wrong (e.g., shows -20°C or 99°C) or fluctuates rapidly.
|
Room Temperature Sensor Short Circuit | View Details |
| E20 |
Thermostat shows E20 and indicates bus power or communication overload on multi-zone systems.
|
Bus Overload / Short Circuit | View Details |
| E3 |
Thermostat displays E3 and underfloor heating or floor protection functions are disabled.
|
Floor Sensor Fault (Open Circuit) | View Details |
| E4 |
Thermostat shows E4 and floor temperature reading is extremely high or low and unstable.
|
Floor Sensor Short Circuit | View Details |
| E5 |
Thermostat displays E5 and cannot control the heating actuator or boiler relay.
|
Output Relay / Triac Fault | View Details |
| E6 |
Thermostat shows E6 and cannot detect or control the wireless receiver or wiring centre.
|
Wireless Communication Failure (Thermostat to Receiver) | View Details |
| E7 |
Thermostat shows E7 and cannot connect to the Danfoss cloud or mobile app; local control may still work.
|
Wi‑Fi / Internet Connectivity Error | View Details |
| E8 |
Thermostat shows E8 and the display may dim or reboot intermittently, especially when calling for heat.
|
Low Supply Voltage / Power Supply Fault | View Details |
| E9 |
Thermostat shows E9 and refuses to operate heating due to detected over-temperature condition.
|
Over-Temperature Protection Triggered | View Details |
| – |
Some rooms controlled by Danfoss smart thermostats are consistently too cold while others are comfortable.
|
Zone Imbalance / Incorrect Balancing | View Details |
| – |
Thermostat backlight or display flickers or dims randomly while powered.
|
Unstable Display Power / Backlight Fault | View Details |
| – |
Thermostat buttons or touchscreen are unresponsive or register incorrect presses.
|
User Interface / Keypad Failure | View Details |
| – |
Thermostat calls for heat (heat icon on), but radiators or underfloor heating remain cold.
|
Heat Demand Not Reaching Boiler or Actuators | View Details |
| – |
Thermostat cannot be discovered or paired with the Danfoss mobile app during setup.
|
App Pairing / Commissioning Failure | View Details |
| – |
Thermostat display is completely blank and unresponsive; heating does not operate.
|
No Power to Thermostat | View Details |
| – |
Thermostat emits a constant or intermittent clicking or buzzing noise during operation.
|
Noisy Relay or Power Electronics | View Details |
| – |
Thermostat frequently cycles the boiler or actuators on and off in short intervals (short cycling).
|
Short Cycling of Heating System | View Details |
| – |
Thermostat frequently shows low battery warnings (for battery-powered Danfoss smart thermostats or wireless sensors).
|
Excessive Battery Drain | View Details |
| – |
Thermostat intermittently disconnects from the Danfoss cloud or app, showing offline status.
|
Intermittent Cloud Connectivity | View Details |
| – |
Thermostat loses time, date, or schedule settings after every power cut.
|
Loss of Time and Schedule After Power Interruption | View Details |
| – |
Thermostat or wiring centre has a noticeable burning smell or visible scorch marks.
|
Overheating / Electrical Damage | View Details |
| – |
Thermostat or wiring centre makes a loud pop and stops working after a lightning storm or power surge.
|
Surge Damage to Electronics | View Details |
| – |
Thermostat overshoots the set temperature by several degrees before turning the heating off.
|
Temperature Overshoot / Poor Control Tuning | View Details |
| – |
Thermostat powers on but does not call for heat even when room temperature is well below setpoint.
|
No Heat Demand from Thermostat | View Details |
| – |
Thermostat shows room temperature that is clearly inaccurate compared to other thermometers.
|
Inaccurate Room Temperature Measurement | View Details |
| – |
Underfloor heating controlled by the thermostat causes floor to feel excessively hot or damages floor covering.
|
Floor Overheating in Underfloor Heating System | View Details |
No matching codes found
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