Navien E047 Fault Code: Causes, Fixes & Repair Costs
What does the Navien E047 fault code mean?
The E047 fault code on a Navien boiler signals that the control board has detected an abnormality with the exhaust thermistor — the sensor responsible for monitoring the temperature of combustion gases as they leave the heat exchanger and travel through the flue. When this sensor produces a reading that falls outside its expected range (due to an open circuit, a short circuit, or an implausibly high or low value), the boiler locks out as a precaution to prevent unsafe flue gas temperatures going undetected. Because the exhaust thermistor is a safety-critical component, the boiler will not resume normal operation until the fault is investigated and cleared.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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.
Common causes
- Faulty or degraded exhaust thermistor Common
Over time the thermistor element itself can drift out of calibration, develop an open circuit, or short internally. When a Gas Safe engineer tests resistance across the sensor with a multimeter, a reading that is significantly outside the manufacturer's specified range confirms the component needs replacing. This is the most frequent root cause of E047.
- Loose or corroded wiring connection Common
The thermistor connects to the PCB via a plug-and-socket harness. Vibration, moisture ingress, or simple age can cause the connector to work loose or the terminals to corrode, producing intermittent or completely absent signals that the board interprets as a fault. An engineer will inspect the connector and the wiring run for damage before condemning the sensor itself.
- PCB communication fault Sometimes
If the wiring and thermistor both check out correctly, the fault may lie on the PCB itself — either a damaged input circuit or a failed analogue-to-digital conversion channel. This is less common but should be considered if a new thermistor does not clear the code.
- Flue restriction or exhaust blockage Sometimes
A partially blocked or incorrectly installed flue can cause abnormally high exhaust temperatures, pushing the thermistor reading outside its safe window and triggering E047 as a protective lockout. This is particularly relevant if the fault appears suddenly rather than developing gradually.
How to fix it
- Check the boiler display and note the exact code DIY safe
Confirm that E047 is shown and not a similar code. Take a photo if helpful — this will save time when you contact an engineer. Make a note of whether the lockout happened suddenly or has been occurring intermittently.
- Attempt a single reset DIY safe
Press the Back (or Reset) button on the Navien control panel as described in your user manual. If the boiler fires up and runs normally, monitor it closely. If the E047 code returns within a short time, do not keep resetting — repeated resets without addressing the cause will not help and may mask the underlying problem.
- Check that your gas supply is working DIY safe
Verify that other gas appliances in the property (hob, oven) are functioning normally. If there is no gas supply, contact your gas supplier rather than an engineer. If gas is available elsewhere, this step is complete.
- Do not remove the boiler casing or touch internal components Gas Safe engineer
The exhaust thermistor and its wiring are located inside the boiler casing. Accessing, testing, or replacing any internal component requires a Gas Safe registered engineer. Opening the casing yourself is unsafe, may void your warranty, and is not permitted for unqualified persons.
- Have a Gas Safe engineer inspect the exhaust thermistor and wiring Gas Safe engineer
An engineer will disconnect the thermistor connector and measure its resistance with a multimeter, comparing the result against Navien's published specification for the relevant model. They will also inspect the wiring harness for signs of burning, corrosion, or mechanical damage, and check that the connector seats firmly at the PCB.
- Replace the exhaust thermistor if confirmed faulty Gas Safe engineer
If resistance values are out of specification or the sensor is visibly damaged, the engineer will fit a replacement thermistor, reconnect the wiring, and clear the fault code before commissioning the boiler. Only Navien-approved or compatible replacement parts should be used to preserve any remaining warranty.
- Inspect the flue system if the thermistor and wiring are sound Gas Safe engineer
Where the thermistor and PCB connections are both found to be in good order, the engineer should check the flue terminal and run for blockages, damage, or incorrect installation that could be causing abnormal exhaust temperatures and triggering the fault.
- Contact a Gas Safe registered engineer if the code persists or recurs Gas Safe engineer
If the E047 code cannot be cleared after professional inspection and thermistor replacement, further diagnostics — including possible PCB investigation — are needed. Always use a Gas Safe registered engineer for any internal boiler work; you can verify registration at gassaferegister.co.uk.
Parts you may need
- Exhaust thermistor (flue gas temperature sensor) · from £25
- Wiring harness connector kit · from £15
- PCB (printed circuit board) — if sensor and wiring are ruled out · from £220
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–£300, depending on the underlying cause.
Frequently asked questions
Can I fix Navien E047 myself by just resetting the boiler?
A single reset is always worth trying and is safe for a homeowner to do. However, E047 is a sensor fault that will almost always return if the underlying issue — a failed thermistor, a loose wiring connection, or a PCB problem — has not been addressed. Repeated resetting without a proper diagnosis is not recommended. Once the code returns after a reset, you need a Gas Safe registered engineer to investigate.
How much does it typically cost to repair a Navien E047 fault in the UK?
For most homeowners, the total cost — covering the engineer's call-out, diagnosis, and thermistor replacement — falls in the range of £120 to £300. If the fault turns out to be a wiring connector issue, the labour cost may be at the lower end. If a PCB replacement is needed, the cost can rise considerably higher (typically £350–£550 all-in), but PCB failure is a much less common outcome. Always get a written quote before work begins.
Will E047 damage my Navien boiler if I leave it?
The E047 lockout is a protective measure — the boiler has shut itself down specifically to prevent it running with a compromised exhaust temperature sensor. Leaving it in lockout will not cause further damage in itself, but you will have no heating or hot water until it is repaired. Avoid attempting to force repeated resets to keep the boiler running, as this circumvents an important safety function.
Does fixing E047 affect my Navien warranty?
Navien's warranty terms generally require that all internal repairs are carried out by a qualified Gas Safe registered engineer using approved parts. Having an unqualified person open the boiler casing or fit non-approved components can invalidate your warranty. Navien also typically requires an annual service by a Gas Safe engineer to keep the warranty valid, so make sure your service records are up to date.