Remeha E4 Fault Code – Ignition Failure
The E4 fault code on Remeha boilers indicates that the boiler has failed to establish a flame after repeated start attempts — typically more than five consecutive tries without any flame being detected. This can be caused by the absence of an ignition spark, a spark that fails to produce a stable flame, or a flame that lights briefly but is not properly detected by the ionisation sensor. The boiler locks out to prevent unburned gas from accumulating, which is why you'll see E4 displayed rather than the boiler simply retrying indefinitely.
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 Remeha E4 fault code mean?
The E4 fault code on Remeha boilers indicates that the boiler has failed to establish a flame after repeated start attempts — typically more than five consecutive tries without any flame being detected. This can be caused by the absence of an ignition spark, a spark that fails to produce a stable flame, or a flame that lights briefly but is not properly detected by the ionisation sensor. The boiler locks out to prevent unburned gas from accumulating, which is why you'll see E4 displayed rather than the boiler simply retrying indefinitely.
Common causes
- Gas supply issue Common
The most common starting point for E4. If the gas meter or isolation valve is off, or there is a temporary interruption to your gas supply, the boiler cannot form a flame no matter how many times it tries. Incorrectly set gas pressure or air trapped in the gas line after supply work can cause exactly the same symptom.
- Ignition electrode fault Common
The ignition electrodes on earlier Remeha models are known to bend out of shape over time, increasing the gap between the electrode tip and the burner. When the gap is too wide, the spark either fails entirely or is too weak to ignite the gas reliably. A failed ignition transformer produces the same result — no spark at all.
- Burner rope seal or combustion door gasket failure Common
A small rope seal sits between the burner and the burner door. When this seal deteriorates, gas can ignite in the wrong location — away from the ionisation probe — so the boiler perceives no flame even though combustion is occurring. Two red rubber combustion door seals can also fail, causing similar misfires. Engineers frequently find that replacing the full service kit (electrode plus all three gaskets) resolves the E4 fault without needing to touch the PCB.
- Low ionisation current or faulty ionisation sensor Sometimes
Even when a flame is present and looks stable, the ionisation sensor must measure a current of between roughly 3 µA and 9 µA to confirm a valid flame. Readings significantly below this range — sometimes as low as 0.2 µA — cause the boiler to cut the flame after just a couple of seconds. This can result from a worn sensor, contamination on the electrode, or incorrect combustion air/gas ratio.
- Frozen or blocked condensate pipe Sometimes
In cold weather, the condensate pipe that runs outside the property can freeze solid. Water then backs up inside the boiler, disrupting combustion and triggering various lockout codes including E4. This is a seasonal but very well-documented cause on Remeha condensing boilers.
- Incorrect CO₂ or combustion calibration Sometimes
If the gas-to-air ratio drifts out of the manufacturer's specified range — producing CO₂ readings above the correct level at both high and low fire — the burner may fail to stabilise and lock out on E4. Recalibrating the gas valve to the correct combustion settings has been shown to restore first-attempt ignition.
- PCB or electronics fault Rare
If all the ignition components and gaskets are in good order, attention turns to the printed circuit board. A known failure mode is a high-value resistor (typically 1 MΩ) in series with the ionisation electrode going open circuit, which means the PCB cannot read any ionisation current regardless of what the flame is actually doing. The PCB should always be investigated last, after mechanical components have been ruled out.
How to fix it
- Check your gas supply is working DIY safe
Before anything else, confirm that other gas appliances in your home — hob, gas fire, or oven — are working normally. If nothing gas-powered is working, contact your gas supplier, as there may be a supply interruption or your meter isolation valve may be closed. There is nothing the boiler itself needs until gas is restored.
- Inspect and thaw a frozen condensate pipe (cold weather only) DIY safe
If the weather is below freezing, locate the plastic condensate pipe that exits your property externally. If it feels solid or is visibly iced over, carefully pour warm (not boiling) water along the length of the pipe until you can hear liquid flowing freely again. Once thawed, try resetting the boiler. Never use a naked flame to thaw pipework.
- Top up system pressure if low DIY safe
Check the pressure gauge on the boiler. It should read between 1.0 bar and 1.5 bar when the system is cold. If it is below 1.0 bar, use the filling loop to top it up slowly to around 1.2–1.3 bar. Low pressure alone is unlikely to cause E4, but it can contribute to unstable operation.
- Reset the boiler DIY safe
Once you have checked the above, press the reset button on the boiler — usually held for a few seconds — and allow it to complete a full start sequence. If it locks out again on E4, repeat once or twice more (no more than two to three resets in quick succession). Repeated unsuccessful resets will not fix the underlying fault and can mask important diagnostic information for an engineer.
- Engineer: inspect and replace ignition electrodes and burner gaskets Gas Safe engineer
A Gas Safe engineer should remove the burner assembly and inspect the ignition electrodes for deformation, cracking, or carbon contamination. A dedicated service kit for Remeha Avanta models includes a new spark electrode and three gaskets — the burner rope seal and two red rubber combustion door seals. Experienced engineers recommend replacing all three gaskets as a matter of course before investigating electronic components, as this resolves the majority of E4 faults on these boilers.
- Engineer: test and calibrate the ignition transformer and ionisation circuit Gas Safe engineer
The engineer should verify that the ignition transformer is generating an adequate spark and that the ionisation current during a live flame falls within the specified 3–9 µA range. A reading significantly below this threshold confirms either a faulty ionisation electrode or a wiring issue between the electrode and PCB.
- Engineer: check and adjust combustion settings (CO₂ calibration) Gas Safe engineer
Using a calibrated flue gas analyser, the engineer should measure CO₂ output at both high and low firing rates and compare the readings against Remeha's specifications. If the gas valve trim screws are out of adjustment, correcting the gas-to-air ratio can resolve ignition instability without any parts being replaced.
- Engineer: test the gas valve Gas Safe engineer
If the ignition system and gaskets are in good order, the engineer should verify that the gas valve is opening correctly and delivering the right gas pressure to the burner. A valve that is sticking or not receiving the correct electrical signal from the PCB will prevent flame formation entirely.
- Engineer: investigate the PCB as a last resort Gas Safe engineer
If all mechanical components have been tested and found serviceable, the PCB becomes the prime suspect. The engineer should check for the known open-circuit resistor failure on the ionisation circuit. PCB replacement is expensive, so a thorough mechanical investigation beforehand is essential to avoid unnecessary parts costs.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If you have carried out the basic homeowner checks and the boiler continues to display E4, do not attempt further investigation yourself. Book a Gas Safe registered engineer who has experience with Remeha appliances. You can verify any engineer's registration at the official Gas Safe Register website before they arrive.
Parts you may need
- Remeha Avanta ignition electrode · from £35
- Burner rope seal (graphite) · from £15
- Combustion door rubber gaskets (pair) · from £20
- Remeha service kit (electrode + 3 gaskets) · from £65
- Ignition transformer · from £55
- Ionisation sensor electrode · from £30
- Gas valve · from £120
- PCB (printed circuit board) · from £280
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 £150–£350, depending on the underlying cause.
Frequently asked questions
Can I reset my Remeha boiler myself when E4 is showing?
Yes, you can reset the boiler yourself — typically by pressing and holding the reset button for a few seconds. However, the E4 code means the boiler has already attempted to fire multiple times without success, so a reset will only help if there was a temporary cause such as a momentary gas supply interruption or a one-off sensor blip. If the boiler locks out again within a short time, further resets will not fix the fault and a Gas Safe engineer should be called.
How much does it cost to fix a Remeha E4 fault in the UK?
For the most common repairs — ignition electrode replacement and burner gasket renewal — most homeowners pay in the region of £150 to £250 including parts and labour. If the gas valve needs replacing, costs typically rise to around £250–£350. A PCB replacement is considerably more expensive, often £350–£500 or above depending on the model and engineer, but this is a last-resort repair after all other components have been ruled out. Labour rates in London and the South East run roughly 20–40% higher than the UK average.
Why does my Remeha boiler light briefly then cut out on E4?
This is a classic sign of a low ionisation current. The burner manages to ignite but the ionisation sensor — which passes a tiny electrical current through the flame to confirm it is present — is not reading a high enough value to satisfy the boiler's control board. Causes include a bent or contaminated electrode, a deteriorated burner rope seal that allows gas to ignite in the wrong location, or, less commonly, a failed resistor on the PCB that handles the ionisation signal. A Gas Safe engineer can measure the ionisation current with appropriate test equipment and pinpoint the cause.
Could a frozen condensate pipe cause an E4 fault on my Remeha boiler?
Yes. During cold snaps, the plastic condensate pipe that carries waste water from the boiler to the drain can freeze solid. When this happens, water backs up inside the boiler and can interfere with the burner and combustion chamber, preventing stable ignition. You can thaw the pipe yourself by pouring warm (not boiling) water over the external section. Once it is clear and the boiler is reset, it should fire normally. If E4 returns after the pipe has thawed, a different underlying fault is present and an engineer is needed.