Remeha E.04.00 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.04.00 fault code mean?
The E.04.00 code belongs to Remeha's E.04 fault family, which covers ignition and flame-establishment failures. When this code appears, the boiler has made multiple attempts to light — typically five or more — without successfully detecting a stable flame, and has locked itself out as a safety precaution. The boiler will not restart automatically; it needs either a manual reset or an underlying fault to be fixed first. The '.00' suffix pinpoints this as the base-level ignition lockout within the E4 category, distinguishing it from related sub-faults (such as E.04.01 or E.04.02) that indicate more specific points of failure in the ignition sequence on certain Remeha models. In all cases the core problem is the same: the boiler cannot confirm a reliable flame is present.
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
- Gas supply interrupted or insufficient Common
If the gas supply to the boiler is turned off, has low pressure, or another appliance has tripped the meter, the burner simply cannot light. This is the first and simplest thing to rule out before assuming anything is broken.
- Faulty or degraded ignition/ionisation electrode Common
The electrode both sparks to ignite the gas and then senses the flame via a tiny ionisation current (typically 3–9 µA). A worn, cracked, or contaminated electrode can fail to spark reliably, or it may detect an ionisation current as low as 0.2 µA — far too weak for the boiler to accept as a confirmed flame — causing it to cut out within seconds and eventually lock out.
- Dirty or partially blocked burner Sometimes
Debris, scale, or combustion residue on the burner surface can disrupt the gas-air mixture, making ignition erratic or impossible. This is more likely on older boilers or those that have not been serviced recently.
- Flue blockage or combustion-gas recirculation Sometimes
A blocked or incorrectly terminated flue, or a flue positioned where exhaust gases are drawn back into the air intake, can deprive the burner of fresh oxygen or flood it with CO₂-rich air. Both conditions prevent a stable flame and trigger lockout.
- Wiring fault or open-circuit electrode lead Sometimes
A high-resistance break — sometimes in a 1 MΩ series resistor on the electrode circuit — can interrupt the ionisation signal even when the electrode itself is fine. Damaged or corroded connecting leads produce the same result.
- Faulty gas valve Rare
If the gas valve fails to open fully, or sticks, the burner receives insufficient gas to sustain ignition. The boiler may spark correctly but still fail to establish a flame.
- PCB (printed circuit board) failure Rare
The PCB controls the entire ignition sequence. A failing board may send incorrect signals to the electrode, misread the ionisation feedback, or fail to open the gas valve at the right moment, producing a lockout that looks identical to an electrode fault.
How to fix it
- Check that your gas supply is working DIY safe
Turn on a gas hob or check another gas appliance in the house. If nothing else is getting gas either, contact your gas supplier — the problem is upstream of the boiler and no amount of resetting will help. If other appliances work normally, the supply to the boiler is likely fine.
- Inspect the condensate pipe for freezing (cold weather only) DIY safe
In sub-zero temperatures the plastic condensate pipe that runs outside can freeze solid, causing the boiler to shut down. Pour warm (not boiling) water along the pipe to thaw it, or use a heat pack. Once thawed, attempt a reset.
- Reset the boiler — once or twice only DIY safe
Press and hold the reset button as described in your Remeha user guide (typically 3–5 seconds). Allow the boiler a full ignition attempt — this can take 30–60 seconds. If it lights and stays on, monitor it closely. If it locks out again immediately, do not keep resetting; repeated forced attempts without fixing the underlying fault can cause further damage and will not resolve an ignition problem.
- A Gas Safe engineer should test the complete ignition sequence Gas Safe engineer
An engineer will run through the full start-up cycle and measure the ionisation current at the electrode to determine whether the spark is forming correctly and whether the flame signal is within the acceptable range (3–9 µA). This single test eliminates most causes quickly.
- Electrode cleaning or replacement Gas Safe engineer
If the ionisation current is low or the electrode shows physical damage, the engineer will clean or replace it. The electrode is located inside the combustion chamber behind the boiler casing — this work requires Gas Safe registration and must not be attempted by a homeowner.
- Burner inspection and cleaning Gas Safe engineer
The engineer will remove and inspect the burner for debris or corrosion. Blocked burner ports are cleaned with appropriate tools; a damaged burner will be replaced. The boiler must be fully isolated from gas and electricity before this work begins.
- Check flue and air-intake paths Gas Safe engineer
The engineer will verify that the flue terminal is clear of obstructions (bird nests, ice, debris) and correctly positioned so that exhaust gases cannot recirculate into the air intake. They will also check the flue for soundness along its full length.
- Test the gas valve operation Gas Safe engineer
Using a manometer, the engineer will confirm that gas pressure at the valve inlet is within the manufacturer's specification and that the valve is opening fully. A valve that is stuck or under-delivering gas must be replaced.
- Inspect the PCB and electrode wiring Gas Safe engineer
If all ignition components test satisfactorily, the engineer will check the electrode lead for high resistance or open-circuit breaks, test the series resistor on the electrode circuit, and evaluate the PCB for fault codes or signs of failure. PCB replacement is a last resort given the cost involved.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Any fault that persists after a couple of resets requires a Gas Safe engineer. Do not continue attempting to run the boiler in lockout. You can find a registered engineer at the Gas Safe Register website (gassaferegister.co.uk).
Parts you may need
- Ignition/ionisation electrode assembly · from £45
- Electrode connecting lead/ignition lead · from £25
- Burner assembly · from £90
- Gas valve · from £120
- PCB (main control 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 £120–£320, depending on the underlying cause.
Frequently asked questions
Can I fix the Remeha E.04.00 fault myself?
The only checks a homeowner can safely carry out are: confirming the gas supply works on other appliances, thawing a frozen condensate pipe in winter, and attempting one or two resets. Everything beyond that — testing the electrode, cleaning the burner, checking the gas valve, or inspecting wiring — requires a Gas Safe registered engineer. Working on gas components without registration is illegal in the UK and potentially dangerous.
How many times should I reset the boiler before calling an engineer?
Reset it once, or at most twice if the first attempt looked promising but it locked out again within a few minutes. If the boiler repeatedly refuses to stay lit, continued resetting will not fix the underlying fault and could mask a more serious problem. Call a Gas Safe engineer at that point.
What does a low ionisation current mean and why does it cause lockout?
After the spark ignites the gas, the boiler uses the same electrode to confirm the flame is genuinely present by measuring a tiny electrical current — typically between 3 µA and 9 µA — that passes through the flame. If the electrode is worn, incorrectly positioned, or the flame is very weak, this current can drop as low as 0.2 µA. The boiler's control board treats anything below its minimum threshold as 'no flame detected' and shuts the gas off within a couple of seconds, leading to a lockout after several failed attempts.
How much does it cost to repair an E.04.00 fault on a Remeha boiler?
Most repairs fall between £120 and £320 including parts and labour. Replacing the ignition or ionisation electrode — the most common fix — typically costs £100–£200 all-in. A gas valve replacement usually comes in around £180–£250. If the PCB turns out to be at fault, costs can rise to £400–£550, at which point it is worth getting a boiler replacement quote alongside the repair quote, particularly if the boiler is more than ten years old.