Navien NCM 1130HH Fault codes & diagnostics

77 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 30 kW 2014-2018 Discontinued

Replaced by: NCB500

Download the Navien NCM 1130HH manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
10 Emergency 55 High 9 Medium 3 Low

All 77 documented codes

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96

Your boiler has detected a minor internal software glitch and has temporarily stopped working to protect itself.

High DIY-safe £100-£250

What to check first

  1. Switch the boiler off at the fused spur or wall switch.
  2. Wait for 60 seconds to allow the internal system to completely reset.
  3. Switch the boiler back on and check if the error code clears.

Parts commonly replaced

  • Main PCB
  • Control Board

Related codes

97

Your boiler has detected an internal software or hardware error that prevents it from operating safely.

High Engineer only £150-350

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Control board

Related codes

98

Your boiler has lost communication with an extra system control module, which usually means the unit cannot coordinate its advanced heating zones properly.

High Engineer only £150-300

Parts commonly replaced

  • Extension module
  • Wiring harness
  • Main control board

Related codes

99

Your boiler has lost communication with an extra control module used to manage complex heating setups or multiple zones.

High Engineer only £150-350

Parts commonly replaced

  • Extension module
  • Wiring harness
  • Main PCB

Related codes

100

Your boiler's digital display and room thermostat are conflicting because they are both trying to control the system time at the same time.

Low Engineer only £90-150

Parts commonly replaced

  • Control Board
  • HMI Display Unit
  • Room Thermostat
102

Your boiler has lost its internal time memory because a backup battery or capacitor has run down, but the heating and hot water should still work normally.

Low Engineer only £100-200

Parts commonly replaced

  • PCB
  • Internal backup battery/capacitor
114

Your boiler has automatically shut down because a safety sensor detected that the exhaust gases leaving the flue are getting too hot.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue gas thermostat
  • Heat exchanger
  • PCB

Related codes

116

Your boiler has automatically shut down because it detected that the exhaust gases leaving the flue are getting too hot.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue gas temperature sensor
  • Main heat exchanger

Related codes

117

Your boiler has detected that the internal water pressure is dangerously too high, which can cause safety valves to open or damage the system.

Emergency DIY-safe £90-180

What to check first

  1. Locate the filling loop valves connected to your boiler.
  2. Ensure both filling loop valves are fully closed and not letting extra water in.
  3. Bleed one or two radiators in your home to release a little water and bring the pressure gauge down to between 1.0 and 1.5 bar.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Filling loop valve

Related codes

118

Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe

What to check first

  1. Locate the filling loop valves underneath your boiler.
  2. Open the valves slightly to let water into the system until the pressure gauge reaches between 1.0 and 1.5 bar.
  3. Close both valves firmly and check the pressure holds steady.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Automatic air vent

Related codes

Showing 11–20 of 77
121

Your heating system is not reaching the expected temperature target, so your radiators may stay lukewarm or fail to warm up properly.

Medium Engineer only £150-350

Parts commonly replaced

  • Flow Temperature Sensor
  • Circulating Pump
  • Motorised Valve

Related codes

122

Your boiler is not reaching the required temperature for your second heating zone, meaning part of your home may not warm up properly.

Medium Engineer only £150-350

Parts commonly replaced

  • Flow Sensor
  • Mixing Valve
  • Circulating Pump
  • PCB

Related codes

127

Your boiler's hot water cylinder has not reached the high temperature required to kill bacteria within the set timeframe.

Medium Engineer only £90-200

Parts commonly replaced

  • Immersion heater
  • NTC temperature sensor
  • Control board

Related codes

157

Your boiler has temporarily stopped working because an internal safety thermostat detected that the water inside the heating pipe has become too hot.

High Engineer only £150-300

Parts commonly replaced

  • Flow thermostat
  • Circulating pump
  • PCB

Related codes

158

Your boiler has temporarily stopped working because the pipe that drains away waste water is blocked or frozen, causing a safety switch to activate.

High DIY-safe £80-150

What to check first

  1. Locate the external condensate pipe outside your home where it empties into a drain.
  2. Check if the pipe is frozen during cold weather by pouring warm (not boiling) water over it to thaw any ice.
  3. Inspect the pipe for any visible kinks, blockages, or sharp bends that might be stopping water from flowing freely.

Parts commonly replaced

  • Condensate trap
  • Condensate pressure switch
  • Internal condensate hose

Related codes

164

Your boiler has detected an issue with the water pressure or flow sensor in the heating system, which causes it to shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Water pressure sensor
  • Flow switch
  • Wiring harness

Related codes

187

Your boiler's computer system has detected an internal settings error and cannot start up safely.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Panel
253

Your boiler has detected a confusing startup signal due to a brief electrical glitch or an internal communication error between its main control boards.

Medium Engineer only £150-350

Parts commonly replaced

  • Boiler Control Unit (BCU)
  • Wiring harness
  • Main PCB

Related codes

254

Your boiler has encountered an unrecognized internal communication error and needs an engineer to inspect the control software.

High Engineer only £150-300

Parts commonly replaced

  • Control board
  • Wiring harness
257

Your boiler has detected an issue with one of its internal temperature sensors, which has temporarily stopped it from working safely.

High Engineer only £150-250

Parts commonly replaced

  • Pack temperature sensor
  • Wiring harness

Related codes

Showing 21–30 of 77
258

Your boiler has temporarily shut down because the internal temperature has risen too high.

High Engineer only £150-350

Parts commonly replaced

  • High limit thermostat
  • Heat exchanger
  • Pump

Related codes

259

Your boiler has detected an internal temperature sensor issue, meaning it cannot accurately measure the heat and has safely shut down to prevent damage.

High Engineer only £150-£300

Parts commonly replaced

  • Temperature Sensor
  • Main PCB

Related codes

260

Your boiler has detected a problem with one of its internal temperature sensors, which means it cannot accurately measure how hot the water is.

Medium Engineer only £120-£250

Parts commonly replaced

  • Heating Circuit Temperature Sensor
  • Wiring Harness

Related codes

261

Your boiler has detected that the burner has unexpectedly gone out while trying to run.

High Engineer only £150-350

Parts commonly replaced

  • Flame sensor
  • Gas valve
  • Ignition electrode

Related codes

262

Your boiler has temporarily stopped working because the secondary burner has lost its flame, meaning you currently have no heating or hot water.

High Engineer only £150-300

Parts commonly replaced

  • Flame electrode
  • Gas valve
  • PCB

Related codes

263

Your boiler has lost communication with its main electronic control unit, meaning it cannot safely start up or operate.

High Engineer only £250-£500

Parts commonly replaced

  • Boiler Control Unit (BCU)
  • Wiring Harness
264

Your boiler has lost internal communication with its main control unit, meaning it has temporarily shut down for safety.

High Engineer only £150-£350

Parts commonly replaced

  • Boiler Control Unit (BCU)
  • Wiring Harness

Related codes

265

Your boiler's main control unit has experienced an internal startup error and cannot safely boot up.

High Engineer only £250-£450

Parts commonly replaced

  • Boiler Control Unit (BCU)
  • Main PCB

Related codes

266

Your boiler has detected that the internal fan responsible for safely clearing exhaust gases is not spinning at the correct speed.

High Engineer only £150-350

Parts commonly replaced

  • Boiler Fan
  • Fan Wiring Harness
  • Printed Circuit Board (PCB)

Related codes

267

Your boiler's internal fan failed to reach the required speed during its startup check, preventing the system from safely igniting.

High Engineer only £150-300

Parts commonly replaced

  • Boiler Fan
  • Printed Circuit Board (BCU)

Related codes

Showing 31–40 of 77
268

Your boiler has detected an issue with an internal valve that regulates water flow, meaning it cannot operate safely and has shut down.

High Engineer only £150-300

Parts commonly replaced

  • Spool valve
  • Gas valve assembly
  • Printed circuit board (PCB)

Related codes

269

Your boiler has detected an internal calibration error with its gas valve during startup, meaning it cannot safely regulate the fuel supply to ignite.

High Engineer only £150-350

Parts commonly replaced

  • Gas Valve
  • PCB

Related codes

270

Your boiler has temporarily stopped because the temperature sensors detected that parts of the heating unit are getting much hotter than others.

High Engineer only £150-350

Parts commonly replaced

  • Heat exchanger
  • NTC temperature sensor
  • Circulating pump

Related codes

271

Your boiler has detected that the water pressure inside the system is currently too high, so it has safely stopped working until the pressure is reduced.

High DIY-safe

What to check first

  1. Locate the filling loop connected to your boiler.
  2. Ensure both valves on the filling loop are firmly closed to stop more water from entering.
  3. Bleed one or two radiators in your home to release trapped air and drain a little water until the pressure gauge drops to the normal 1 to 1.5 bar range.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Pressure sensor

Related codes

272

Your boiler has detected that the water pressure inside the system is too low for it to operate safely.

High Engineer only £90-200

Parts commonly replaced

  • Differential pressure switch
  • Pressure sensor
  • Condensate trap

Related codes

273

Your boiler has detected an internal disagreement or configuration issue with the water pressure sensor, causing it to lock out for safety.

Medium Engineer only £150-300

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

274

Your boiler has detected that water is dangerously low or missing inside the system, and has shut down to prevent severe internal damage.

High Engineer only £150-350

Parts commonly replaced

  • Water pressure sensor
  • Circulating pump
  • Flow switch

Related codes

275

Your boiler has detected an issue with water flow while trying to remove air from the system, which temporarily stops it from working properly.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Automatic air vent
  • Circulating pump

Related codes

276

Your boiler has stopped working because it cannot detect enough water flowing through the system to operate safely.

High Engineer only £150-£350

Parts commonly replaced

  • Water flow sensor
  • Circulating pump
  • Automatic bypass valve

Related codes

277

Your boiler is not detecting any water flowing through the system when you try to run the hot tap, so it cannot switch on to heat the water.

High Engineer only £120-250

Parts commonly replaced

  • Flow sensor
  • DHW flow switch
  • Wiring harness

Related codes

Showing 41–50 of 77
278

Your boiler is temporarily shutting down because the water inside is getting too hot, usually caused by a blockage in water flow.

High Engineer only £150-300

Parts commonly replaced

  • Circulator pump
  • Heat exchanger
  • NTC thermistor

Related codes

280

Your boiler has detected that the temperature inside the main heat exchanger has become dangerously high and has automatically shut down to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • Temperature sensor
  • Heat exchanger
  • Circulating pump
  • PCB

Related codes

281

Your boiler has detected an issue with its internal dynamic absorber component and has temporarily stopped working for safety.

High Engineer only £150-300

Parts commonly replaced

  • Dynamic absorber
  • PCB
282

Your boiler has detected an internal safety or ignition system communication fault and has safely locked itself out to prevent unsafe operation.

High Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • PCB
  • Ignition lead

Related codes

283

Your boiler has detected an electrical overload in one of its internal components, causing the system to stop working to protect itself.

High Engineer only £150-350

Parts commonly replaced

  • PCB
  • Internal wiring
  • Pump or fan

Related codes

284

Your boiler has temporarily stopped working because an internal safety sensor has detected that the water temperature is getting too hot.

High Engineer only £150-350

Parts commonly replaced

  • Water temperature sensor
  • Water circulation pump
  • Heat exchanger

Related codes

285

Your boiler has detected an electrical short circuit on the internal circuit board or main wiring connection.

Emergency Engineer only £200-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

286

Your boiler has safely shut down because the internal engine head has become too hot.

Emergency Engineer only £150-350

Parts commonly replaced

  • Circulation pump
  • Temperature sensor
  • Heat exchanger

Related codes

287

Your boiler has detected that the temperature inside the main engine head is too low, which prevents it from operating safely.

High Engineer only £150-350

Parts commonly replaced

  • Temperature sensor
  • Thermostat
  • Control board

Related codes

288

Your boiler has temporarily stopped working because it has detected an excessively high temperature inside its internal cleaning or heat recovery system.

High Engineer only £150-350

Parts commonly replaced

  • Temperature sensor
  • Circulation pump
  • PCB

Related codes

Showing 51–60 of 77
289

Your boiler has detected that the internal components are getting too hot, so it has safely shut down to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • Water temperature sensor
  • Heat exchanger
  • Circulating pump

Related codes

290

Your boiler has detected that a safety or temperature control sensor is overheating, so it has automatically shut down to protect itself.

High Engineer only £150-300

Parts commonly replaced

  • Water temperature sensor
  • High limit thermostat
  • Wiring harness

Related codes

291

Your boiler has detected that a safety temperature sensor has been triggered because the system has gotten too hot.

Emergency Engineer only £150-300

Parts commonly replaced

  • High limit thermostat (G83)
  • NTC temperature sensor
  • Main printed circuit board (PCB)

Related codes

292

Your boiler has detected an issue with the water temperature safety controls and will temporarily stop working to prevent overheating.

High Engineer only £150-300

Parts commonly replaced

  • Temperature sensor
  • High limit thermostat
  • Main printed circuit board

Related codes

293

Your boiler has detected an internal water temperature or circulation safety issue and has temporarily shut down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Water circulation sensor
  • Flow sensor
  • Main PCB

Related codes

294

Your boiler has detected that the burner head is running much hotter than it should be and has automatically shut down to protect itself.

High Engineer only £150-300

Parts commonly replaced

  • Burner gasket
  • Heat exchanger
  • Temperature sensor

Related codes

295

Your boiler has detected an internal combustion or water circulation issue that requires a qualified engineer to inspect and resolve safely.

High Engineer only £150-300

Parts commonly replaced

  • Water Control Sensor
  • Burner Head
  • PCB

Related codes

296

Your boiler has detected an issue with the weather compensation sensor regulation, meaning it may not be adjusting its temperature correctly based on the outside weather.

Low Engineer only £90-180

Parts commonly replaced

  • Weather compensation sensor
  • Wiring harness
  • PCB

Related codes

298

Your boiler has temporarily stopped because a sensor inside detected a flame when the burner should actually be switched off.

High Engineer only £150-300

Parts commonly replaced

  • Flame sensor
  • Printed Circuit Board (PCB)

Related codes

299

Your boiler's secondary burner sensor is incorrectly registering a flame when the burner is actually turned off.

Medium Engineer only £100-250

Parts commonly replaced

  • Ionisation electrode
  • Printed Circuit Board (PCB)

Related codes

Showing 61–70 of 77
300

Your boiler has detected that a key internal part is much colder than it should be, which safely shuts down the system to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Temperature sensor
  • Engine head control board
  • Wiring harness

Related codes

301

Your boiler has automatically shut down because the internal engine head has reached an dangerously high temperature.

Emergency Engineer only £150-350

Parts commonly replaced

  • Temperature sensor
  • Cooling pump
  • Engine head assembly

Related codes

302

Your boiler has detected a dangerous temperature mismatch between its internal sensors, meaning it is not heating safely.

Emergency Engineer only £150-350

Parts commonly replaced

  • Limit Thermocouple
  • Engine Head Control Thermocouple
  • Main Control Board

Related codes

303

Your boiler has detected an internal temperature sensor failure, meaning it cannot properly monitor its own performance and has safely shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Thermocouple
  • Engine head control assembly
  • Wiring harness

Related codes

304

Your boiler has detected a safety sensor issue near the main burner, which causes it to shut down to prevent overheating.

High Engineer only £150-300

Parts commonly replaced

  • Engine head limit thermocouple
  • Thermal fuse assembly
  • Wiring harness

Related codes

305

Your boiler's internal computer is failing to communicate properly with the main burner unit during startup.

High Engineer only £150-350

Parts commonly replaced

  • Wiring harness
  • PCB
  • Burner control unit

Related codes

306

Your boiler is failing to communicate properly with its internal monitoring systems when trying to start up.

High Engineer only £150-300

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

307

Your heating system has temporarily stopped running correctly while trying to operate independently from the main electricity grid.

High Engineer only £150-350

Parts commonly replaced

  • Control board
  • Generator unit
  • Inverter

Related codes

308

Your boiler has detected an internal electronic safety check failure, meaning it has safely shut down to prevent incorrect operation.

High Engineer only £150-300

Parts commonly replaced

  • Main PCB
309

Your boiler has detected an interruption in its electrical power supply.

Medium DIY-safe £90-180

What to check first

  1. Check that the boiler's fused spur switch on the wall is turned on.
  2. Check your home's main fuse box (consumer unit) to see if a trip switch has activated.
  3. Reset the boiler by turning it off and on again if power was recently restored.

Parts commonly replaced

  • Main PCB
  • Fuse
  • Power Supply Unit

Related codes

Showing 71–77 of 77
310

Your boiler has lost communication with its internal electricity-measuring meter, which usually points to an internal wiring or control board problem.

High Engineer only £150-£350

Parts commonly replaced

  • Wiring harness
  • Power meter module
  • Main printed circuit board (PCB)

Related codes

311

Your boiler has lost communication with its external control system or smart thermostat.

Medium Engineer only £100-250

Parts commonly replaced

  • Main PCB
  • External Controller
  • Wiring Harness

Related codes

319

Your boiler has stopped working because a software update on the internal control system was interrupted or failed.

High Engineer only £100-250

Parts commonly replaced

  • PCB
  • Control Board

Related codes

394

Your boiler has lost its internal connection, meaning the main computer cannot talk to the burner control unit.

High Engineer only £150-300

Parts commonly replaced

  • Wiring harness
  • Burner Control Unit (BCU)
  • Main PCB

Related codes

395

Your boiler has temporarily lost its internal connection, meaning it cannot properly talk to its main control unit to start up safely.

High Engineer only £150-350

Parts commonly replaced

  • BCU Control Board
  • Wiring harness

Related codes

396

Your boiler has detected a broken connection or freezing temperature at its internal temperature sensor, causing it to safely shut down.

High Engineer only £150-£300

Parts commonly replaced

  • Temperature sensor
  • Wiring harness
  • Main Control Board (MCB)
397

Your boiler has detected an issue with its internal temperature monitoring startup checks before connecting to the power grid.

High Engineer only £150-300

Parts commonly replaced

  • Temperature sensor
  • Wiring harness
  • PCB