De Dietrich Furnaces Error Codes

A01

Burner does not ignite, furnace attempts ignition then locks out with A01 on display

Ignition Failure Lockout

A02

Burner lights briefly then goes out, repeated attempts then A02 lockout on display

Flame Loss During Operation

A03

Boiler stops with A03, burner off, overheat symbol may be lit

Safety Overheat Thermostat Tripped

A04

Boiler displays A04 and will not start, often after power interruption

Low Water Pressure / Water Shortage

A05

Boiler shows A05, fan may run briefly then stop, no ignition

Air Pressure Switch / Flue Safety Fault

A06

Display shows A06, boiler stops, often associated with domestic hot water demand

Flow Sensor / DHW Sensor Fault

A07

Boiler displays A07, heating stops, flow temperature reading abnormal

Flow Temperature Sensor Fault

A08

Boiler shows A08, no heating, return temperature reading abnormal

Return Temperature Sensor Fault

A09

Boiler locks out with A09, often after long operation at high temperature

Flue Gas Overtemperature / Safety Thermostat

A10

Boiler shows A10, burner off, fan may continue to run

Flame Detection Error (False Flame or No Flame Signal)

A11

Boiler displays A11, no ignition, fan may not start

Fan Start Failure

A12

Boiler shows A12, intermittent burner operation, sometimes with noise from fan

Fan Speed / Airflow Regulation Fault

A13

Boiler displays A13, no heating, pump symbol may flash

Circulation Pump Fault

A14

Boiler shows A14, heating limited or stopped, often with high return temperature

Insufficient Circulation / Delta T Fault

A15

Boiler displays A15, no response to thermostat, heating demand not recognised

External Control / Thermostat Communication Fault

A16

Boiler shows A16, domestic hot water priority fault, DHW not available

3-Way Valve / Diverter Valve Fault

A17

Boiler displays A17, no hot water from storage tank, but heating may work

Cylinder Temperature Sensor Fault

A18

Boiler shows A18, burner output limited, possible modulation issues

Gas Valve Modulation Fault

A19

Boiler displays A19, anti-freeze or low temperature protection fault

Frost Protection / Low Temperature Sensor Fault

A20

Boiler shows A20, general safety lockout, no specific sub-code

General Safety Lockout

E01

Control panel shows E01, boiler unresponsive, display may be blank or frozen

Main PCB / Control Board Fault

E02

Boiler shows E02, no display backlight or intermittent display

User Interface / Display Board Fault

E03

Boiler shows E03, external safety device open (e.g., flue thermostat, safety chain)

External Safety Circuit Open

E04

Boiler displays E04, condensate alarm, boiler stops

Condensate Drain Fault

E05

Boiler shows E05, gas supply error, no ignition

Gas Supply / Gas Valve Error

E06

Boiler displays E06, communication error with remote controller or cascade manager

BUS Communication Fault

E07

Boiler shows E07, external sensor fault (e.g., outdoor sensor)

Outdoor Temperature Sensor Fault

E08

Boiler displays E08, expansion vessel / pressure fluctuation fault

Expansion Vessel / Pressure Regulation Fault

E09

Boiler shows E09, safety valve discharge detected (if sensor fitted) or frequent pressure drops

Safety Valve / Overpressure Fault

E10

Boiler displays E10, internal temperature sensor or limit fault

Internal Boiler Temperature Monitoring Fault

Symptom

Domestic hot water temperature fluctuates between too hot and too cold during shower

Unstable DHW Temperature Control

Symptom

Furnace causes frequent tripping of the household circuit breaker or RCD

Electrical Short or Earth Leakage

Symptom

Furnace condensate pipe drips or gurgles loudly, with occasional water backing up into boiler

Condensate Drainage Problem

Symptom

Furnace does not respond to room thermostat, stays off even when there is demand

Control Signal Not Reaching Boiler

Symptom

Furnace emits a high-pitched whistling or howling noise during operation

Combustion Resonance / Gas Flow Noise

Symptom

Furnace frequently cycles on and off with short run times, causing wear and noise

Short Cycling

Symptom

Furnace is leaking water from the bottom of the casing

Internal Water Leak

Symptom

Furnace is running but radiators are only lukewarm and house does not reach set temperature

Underheating / Insufficient Output

Symptom

Furnace makes loud banging or knocking noises when starting or stopping

Water Hammer / Thermal Expansion Noise

Symptom

Furnace produces a burning or plastic smell when running

Overheating Electrical Component or Dust Burn-off

Symptom

Furnace produces a strong smell of gas near the unit, especially at startup or shutdown

Gas Leak or Incomplete Ignition

Symptom

Furnace runs but some radiators remain completely cold

System Imbalance / Air Lock

Symptom

Furnace starts normally but shuts down after a few minutes without error code

Soft Lockout / Demand Loss

Symptom

Radiators are hot at the top but cold at the bottom, furnace runs continuously

Sludge / Poor Heat Transfer in Emitters