Navien E012 Fault Code: Flame Loss During Operation
The E012 code appears on Navien boilers when the unit fires up successfully but then loses its flame mid-operation and shuts down as a safety precaution. Rather than the boiler failing to ignite at all, the burner lights and then unexpectedly extinguishes — the boiler's control board detects the missing flame signal and locks out to prevent unburned gas from accumulating. This is a safety-driven lockout that should not be repeatedly reset without identifying and resolving the underlying cause.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
What does the Navien E012 fault code mean?
The E012 code appears on Navien boilers when the unit fires up successfully but then loses its flame mid-operation and shuts down as a safety precaution. Rather than the boiler failing to ignite at all, the burner lights and then unexpectedly extinguishes — the boiler's control board detects the missing flame signal and locks out to prevent unburned gas from accumulating. This is a safety-driven lockout that should not be repeatedly reset without identifying and resolving the underlying cause.
Common causes
- Low or fluctuating gas supply pressure Common
A sudden drop in gas pressure — whether caused by high demand on the local network, a partly closed service valve, or an issue at the meter — can starve the burner of fuel mid-cycle. The flame weakens and extinguishes, triggering E012. This is one of the most frequently identified causes in UK engineer call-outs.
- Dirty or degraded flame rod (flame sensor) Common
The flame rod is a small electrode that detects the presence of a flame by measuring a tiny electrical current produced during combustion. Over time, combustion deposits build up on the rod, effectively insulating it and preventing it from relaying an accurate signal to the PCB. The boiler interprets this as flame loss and shuts down — even if the burner is technically still alight.
- Blocked or restricted flue or air intake Common
The flue exhaust terminal and the fresh-air intake pipe are both vulnerable to obstruction from bird nesting material, leaves, compacted debris, or ice forming in cold weather. When exhaust gases cannot escape efficiently, or when combustion air cannot enter freely, the air-to-fuel ratio is disrupted and the flame becomes unstable. This is especially common in autumn and winter.
- Frozen or blocked condensate pipe Sometimes
During cold snaps, the plastic condensate pipe that runs externally can freeze solid. This causes condensate to back up inside the boiler, disrupting normal operation and potentially triggering flame instability as the unit struggles to run correctly. A classic winter fault across northern England and Scotland.
- Faulty or sticking gas valve Sometimes
The gas valve controls the precise flow of gas to the burner. If it begins to stick, wear internally, or fail to hold a consistent flow rate, the burner receives an irregular supply and the flame becomes unstable or goes out entirely. A gas valve fault will persist regardless of resets and requires engineer diagnosis.
- Moisture or internal condensation affecting ignition components Sometimes
Water ingress, a minor internal leak, or heavy condensation accumulating near the ignition electrodes or flame rod wiring can cause intermittent faults. Wet components disrupt the electrical signals involved in flame detection, producing sporadic E012 errors that may clear temporarily only to return.
- Faulty PCB flame-sensing circuit Rare
If the PCB's own flame-sensing circuitry develops a fault — rather than the flame rod itself — the board may report flame loss even when combustion is normal. This is typically diagnosed only after all other causes have been ruled out, as PCB replacement is relatively costly.
How to fix it
- Check that your gas supply is working DIY safe
Before doing anything else, confirm that other gas appliances in the property — a gas hob, a gas fire, or a separate cooker — are operating normally. If nothing gas-powered is working, the issue may be with your meter, a closed service valve, or a wider network outage. Contact your gas supplier if you suspect a supply interruption.
- Thaw a frozen condensate pipe (cold weather only) DIY safe
If temperatures have dropped below freezing and the condensate pipe runs externally, it may be frozen solid. Carefully pour warm (not boiling) water over the visible external section of the pipe until it clears. Do not use a naked flame or kettle-boiling water, as this can crack the pipe. Once thawed, attempt a reset.
- Inspect the flue and air intake terminals for obstructions DIY safe
Go outside and locate the flue exhaust and fresh-air intake terminals on the exterior wall. Check visually for any obvious blockage — nesting material, leaves, ice, or debris packed around the opening. Do not attempt to poke tools into the flue internally. If you can safely clear loose debris from the external terminal without reaching inside the boiler or flue pipe, do so. If you suspect an internal blockage, leave this to an engineer.
- Reset the boiler (no more than twice) DIY safe
Use the reset button or power-cycle the boiler by turning it off at the electrical isolator for around 30 seconds, then switching it back on. Allow the boiler to attempt a full ignition cycle. If it locks out again with E012, perform one further reset. If the fault returns after two resets, stop — repeated resets without fixing the root cause can cause additional wear on ignition components and may affect your warranty.
- Have a Gas Safe engineer test gas inlet and manifold pressure Gas Safe engineer
An engineer will connect pressure gauges to measure the gas supply pressure both at rest and during a live firing cycle. If pressure drops significantly during operation, there is either a supply issue from the meter or network, or a faulty internal gas valve restricting flow. The engineer will advise on the appropriate remedy.
- Have the flame rod inspected, cleaned, or replaced Gas Safe engineer
A Gas Safe engineer will remove the flame rod, inspect it for carbon fouling or physical damage, and either clean the electrode surface or replace the component. They will also check the wiring from the flame rod back to the PCB for signs of corrosion or loose connections.
- Have the flue system professionally inspected and cleaned Gas Safe engineer
An engineer can use appropriate equipment to check for partial blockages further into the flue run that are not visible from outside. They will also verify that the flue termination position complies with current regulations and that the air-to-fuel ratio and combustion readings are within safe limits.
- Have the gas valve assessed and replaced if necessary Gas Safe engineer
If gas pressure and combustion air are confirmed to be correct but the fault persists, the engineer will test the gas valve operation. A valve that is sticking or delivering inconsistent flow will need to be replaced — this is gas-component work and must only be carried out by a Gas Safe registered engineer.
- Have the PCB flame-sensing circuit diagnosed Gas Safe engineer
As a final diagnostic step, if all components have been checked and are functioning correctly, a Gas Safe engineer or Navien-experienced technician will assess whether the PCB's flame detection circuitry is at fault. PCB replacement is a last resort and is usually only recommended once all other causes are definitively ruled out.
- Call a Gas Safe registered engineer if the fault persists or recurs Gas Safe engineer
If E012 returns after your DIY checks, or if you are in any doubt, book a Gas Safe registered engineer promptly. Persistent flame loss can indicate combustion instability which, left unresolved, carries a risk of carbon monoxide production. Do not continue running the boiler through repeated resets without a proper investigation.
Parts you may need
- Navien flame rod (flame sensor electrode) · from £35
- Navien gas valve · from £180
- Navien PCB (main control board) · from £320
- Condensate pipe replacement section and fittings · from £25
- Navien ignition electrode assembly · from £45
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£350, depending on the underlying cause.
Frequently asked questions
Is the Navien E012 code dangerous?
It can indicate a risk if it recurs frequently without investigation. The boiler shuts down as a safety measure to prevent unburned gas from accumulating — so the lockout itself is protective. However, the underlying cause, particularly if related to combustion instability or a partial flue blockage, can create conditions that increase carbon monoxide risk if the boiler is forced to keep running. If E012 keeps returning, stop resetting and call a Gas Safe engineer.
Can I fix E012 myself?
A handful of checks are safe for a homeowner: confirming the gas supply is on, thawing a frozen condensate pipe in cold weather, visually clearing debris from the external flue terminal, and resetting the boiler once or twice. Beyond that, diagnosing and fixing the cause — gas pressure testing, flame rod replacement, gas valve work — must be done by a Gas Safe registered engineer. Tampering with gas components without registration is illegal in the UK and extremely dangerous.
How much does it typically cost to fix Navien E012 in the UK?
For the most common causes, most UK homeowners pay somewhere between £120 and £350. A gas pressure check and adjustment typically costs around £100–£200, a flame sensor clean or replacement sits around £150–£250, and a professional flue inspection usually falls in a similar range. If a gas valve needs replacing you could be looking at £250–£400 including parts and labour. In the less common scenario that the PCB requires replacement, costs can reach £400–£600 or beyond — if you are facing that level of spend on an older Navien boiler, it is worth getting a new boiler quote for comparison.
Why does my Navien boiler show E012 only in cold weather?
Cold-weather E012 faults are most often caused by a frozen condensate pipe. When the external section of the condensate pipe ices over, wastewater backs up inside the boiler and disrupts normal operation. Thaw the pipe gently using warm water poured over the external section, then reset the boiler. If this resolves it, consider insulating the exposed pipe to prevent a recurrence next winter. Persistent cold-weather faults that do not clear after thawing may point to a flue terminal icing issue or low gas pressure on a heavily loaded local network, both of which need engineer investigation.