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