NTI
NTI Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E01
Boiler will not ignite; display shows E01 shortly after a call for heat or domestic hot water
Ignition Failure Lockout
E02
Boiler attempts to start but shuts down with E02; fan may run briefly, no sustained flame
Flame Detection Failure
E03
Boiler locks out with E03; fan may not start or stops quickly; no ignition attempt
Air Pressure Switch / Fan Proving Fault
E04
Boiler shuts down with E04; display may indicate overheat or high limit; unit very hot to touch
High Limit Overheat Trip
E05
Boiler displays E05 and will not fire; may occur after power outage or wiring work
Low Water Pressure / Water Sensor Fault
E06
Boiler shows E06; burner shuts down; may be accompanied by very hot supply temperature
Supply Temperature Sensor (NTC) Fault
E07
Boiler displays E07; may run briefly then shut down; return temperature reading is erratic
Return Temperature Sensor (NTC) Fault
E08
Boiler shows E08 and stops; flue temperature reading is abnormally high or low
Flue Gas Temperature Sensor Fault / Overtemperature
E09
Boiler locks out with E09; may indicate fan speed or RPM error on display
Combustion Fan Speed / RPM Fault
E10
Boiler shows E10; domestic hot water (DHW) may not function correctly
DHW Temperature Sensor Fault
E11
Boiler displays E11; no response to thermostat call; control appears unresponsive or frozen
Control Board Communication / Internal Fault
E12
Boiler shows E12; may be labeled as gas valve error or modulation fault
Gas Valve Modulation / Control Fault
E13
Boiler locks out with E13; may indicate ionization current too low or unstable flame
Weak Flame Signal / Ionization Fault
E14
Boiler shows E14; may be associated with condensate or flue issues; unit shuts down
Condensate Drain / Blockage Fault
E15
Boiler displays E15; may indicate low 24V or power supply fault; intermittent resets
Low Voltage / Power Supply Fault
E16
Boiler shows E16; outdoor reset not functioning correctly; temperatures not adjusting with weather
Outdoor Temperature Sensor Fault
E17
Boiler displays E17; may indicate flow switch or flow sensor error; unit may overheat or short cycle
System Flow Sensor / Flow Switch Fault
E18
Boiler shows E18; DHW does not start or stops unexpectedly during use
DHW Flow Switch / Flow Sensor Fault
E19
Boiler displays E19; may indicate fan communication or PWM error; fan may run at fixed speed only
Fan Communication / Control Signal Fault
E20
Boiler shows E20; may be labeled as safety chain open; unit will not start
Safety Circuit Open (Limit / Cutoff Chain)
Symptom
Boiler cabinet or nearby piping vibrates excessively during operation
Vibration / Mechanical Noise
Symptom
Boiler cycles on and off when only a small zone or single radiator is calling for heat
Low Load / Minimum Firing Rate Mismatch
Symptom
Boiler display backlight is on but text is unreadable or missing segments
Display / User Interface Failure
Symptom
Boiler display shows normal operation but thermostats do not call for heat or boiler does not respond to call
Control / Thermostat Interface Problem
Symptom
Boiler emits exhaust smell or flue gas odor near the unit
Flue Gas Leakage
Symptom
Boiler frequently loses pressure over days or weeks without obvious leaks
Slow Pressure Loss
Symptom
Boiler frequently reaches high pressure and discharges water from relief valve
Over‑Pressurization
Symptom
Boiler ignites with a loud boom or pop sound
Delayed Ignition
Symptom
Boiler leaking water from bottom of cabinet or around piping connections
System Water Leak
Symptom
Boiler makes loud banging or knocking noises when starting or during operation
Kettling / Water Hammer / Expansion Noise
Symptom
Boiler runs but house does not reach set temperature; heat output seems low
Insufficient Heat Output
Symptom
Boiler runs but produces visible white steam or excessive condensation at vent termination
Condensation / Venting Appearance Issue
Symptom
Boiler short cycles, turning on and off frequently without maintaining steady temperature
Short Cycling / Control or Sizing Issue
Symptom
Boiler will not start at all; display is blank or completely off
No Power / Dead Control
Symptom
Boiler’s condensate trap repeatedly fills and overflows or trips safety
Chronic Condensate Drainage Problem
Symptom
Domestic hot water temperature fluctuates or runs hot then cold during a shower
Unstable DHW Temperature
Symptom
Radiators or in‑floor loops are not heating even though boiler appears to run
No Heat to Emitters / Circulation Problem
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Boiler will not ignite; display shows E01 shortly after a call for heat or domestic hot water
|
Ignition Failure Lockout | View Details |
| E02 |
Boiler attempts to start but shuts down with E02; fan may run briefly, no sustained flame
|
Flame Detection Failure | View Details |
| E03 |
Boiler locks out with E03; fan may not start or stops quickly; no ignition attempt
|
Air Pressure Switch / Fan Proving Fault | View Details |
| E04 |
Boiler shuts down with E04; display may indicate overheat or high limit; unit very hot to touch
|
High Limit Overheat Trip | View Details |
| E05 |
Boiler displays E05 and will not fire; may occur after power outage or wiring work
|
Low Water Pressure / Water Sensor Fault | View Details |
| E06 |
Boiler shows E06; burner shuts down; may be accompanied by very hot supply temperature
|
Supply Temperature Sensor (NTC) Fault | View Details |
| E07 |
Boiler displays E07; may run briefly then shut down; return temperature reading is erratic
|
Return Temperature Sensor (NTC) Fault | View Details |
| E08 |
Boiler shows E08 and stops; flue temperature reading is abnormally high or low
|
Flue Gas Temperature Sensor Fault / Overtemperature | View Details |
| E09 |
Boiler locks out with E09; may indicate fan speed or RPM error on display
|
Combustion Fan Speed / RPM Fault | View Details |
| E10 |
Boiler shows E10; domestic hot water (DHW) may not function correctly
|
DHW Temperature Sensor Fault | View Details |
| E11 |
Boiler displays E11; no response to thermostat call; control appears unresponsive or frozen
|
Control Board Communication / Internal Fault | View Details |
| E12 |
Boiler shows E12; may be labeled as gas valve error or modulation fault
|
Gas Valve Modulation / Control Fault | View Details |
| E13 |
Boiler locks out with E13; may indicate ionization current too low or unstable flame
|
Weak Flame Signal / Ionization Fault | View Details |
| E14 |
Boiler shows E14; may be associated with condensate or flue issues; unit shuts down
|
Condensate Drain / Blockage Fault | View Details |
| E15 |
Boiler displays E15; may indicate low 24V or power supply fault; intermittent resets
|
Low Voltage / Power Supply Fault | View Details |
| E16 |
Boiler shows E16; outdoor reset not functioning correctly; temperatures not adjusting with weather
|
Outdoor Temperature Sensor Fault | View Details |
| E17 |
Boiler displays E17; may indicate flow switch or flow sensor error; unit may overheat or short cycle
|
System Flow Sensor / Flow Switch Fault | View Details |
| E18 |
Boiler shows E18; DHW does not start or stops unexpectedly during use
|
DHW Flow Switch / Flow Sensor Fault | View Details |
| E19 |
Boiler displays E19; may indicate fan communication or PWM error; fan may run at fixed speed only
|
Fan Communication / Control Signal Fault | View Details |
| E20 |
Boiler shows E20; may be labeled as safety chain open; unit will not start
|
Safety Circuit Open (Limit / Cutoff Chain) | View Details |
| – |
Boiler cabinet or nearby piping vibrates excessively during operation
|
Vibration / Mechanical Noise | View Details |
| – |
Boiler cycles on and off when only a small zone or single radiator is calling for heat
|
Low Load / Minimum Firing Rate Mismatch | View Details |
| – |
Boiler display backlight is on but text is unreadable or missing segments
|
Display / User Interface Failure | View Details |
| – |
Boiler display shows normal operation but thermostats do not call for heat or boiler does not respond to call
|
Control / Thermostat Interface Problem | View Details |
| – |
Boiler emits exhaust smell or flue gas odor near the unit
|
Flue Gas Leakage | View Details |
| – |
Boiler frequently loses pressure over days or weeks without obvious leaks
|
Slow Pressure Loss | View Details |
| – |
Boiler frequently reaches high pressure and discharges water from relief valve
|
Over‑Pressurization | View Details |
| – |
Boiler ignites with a loud boom or pop sound
|
Delayed Ignition | View Details |
| – |
Boiler leaking water from bottom of cabinet or around piping connections
|
System Water Leak | View Details |
| – |
Boiler makes loud banging or knocking noises when starting or during operation
|
Kettling / Water Hammer / Expansion Noise | View Details |
| – |
Boiler runs but house does not reach set temperature; heat output seems low
|
Insufficient Heat Output | View Details |
| – |
Boiler runs but produces visible white steam or excessive condensation at vent termination
|
Condensation / Venting Appearance Issue | View Details |
| – |
Boiler short cycles, turning on and off frequently without maintaining steady temperature
|
Short Cycling / Control or Sizing Issue | View Details |
| – |
Boiler will not start at all; display is blank or completely off
|
No Power / Dead Control | View Details |
| – |
Boiler’s condensate trap repeatedly fills and overflows or trips safety
|
Chronic Condensate Drainage Problem | View Details |
| – |
Domestic hot water temperature fluctuates or runs hot then cold during a shower
|
Unstable DHW Temperature | View Details |
| – |
Radiators or in‑floor loops are not heating even though boiler appears to run
|
No Heat to Emitters / Circulation Problem | View Details |
No matching codes found
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