Remeha E.04.01 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.04.01 fault code mean?
The E.04.01 code — shown as E04 on older Remeha Avanta displays — means the boiler has entered an ignition lockout. It fires this fault after five consecutive failed start attempts without detecting a stable flame. At that point the boiler shuts itself down and holds in a safe state until the problem is resolved or the unit is reset. The root cause falls into one of three broad categories: no spark being produced, a spark occurring but no flame forming, or a flame establishing briefly but the ionisation signal being too weak for the control board to trust it. Because unburnt gas is involved, the boiler is right to lock out rather than keep trying.
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
- Worn or dirty ignition electrode Common
The ignition electrode produces the spark that lights the burner. With age the tip can erode, bend out of alignment, or become coated in combustion deposits, all of which weaken the spark or prevent it entirely. This is the single most frequent cause of E.04.01 on Remeha appliances.
- Faulty ionisation probe or flame sensor Common
Once lit, the flame must be verified by the ionisation probe. If the probe is coated in soot, cracked, or poorly positioned, the PCB never receives a satisfactory signal and declares a flame failure even when gas has actually ignited — triggering lockout.
- Interrupted or low gas supply Common
If the gas meter isolation valve is partially closed, a prepayment meter has run out of credit, or there is low pressure in the supply network, the boiler cannot receive enough gas to sustain combustion. Always worth checking other gas appliances first.
- Frozen condensate pipe (winter) Sometimes
In cold weather the plastic condensate discharge pipe can freeze and block, causing the boiler to fault on a related error that may present alongside or instead of E.04.01. A blockage backs up condensate into the heat exchanger and can interrupt normal ignition sequences.
- Flue or combustion air seal fault Sometimes
Leaking seals on the combustion door, burner, or flue connections allow exhaust gases to recirculate back into the air intake. This dilutes the combustion air and makes reliable ignition difficult, or causes the flame to fail shortly after lighting.
- Gas valve failure Sometimes
If the gas valve does not open fully — or at all — when the PCB commands it, no fuel reaches the burner. The boiler sparks normally but no flame forms. Gas valve faults are less common than electrode issues but occur as the appliance ages.
- PCB or ignition transformer fault Rare
The PCB orchestrates the entire firing sequence: it starts the fan, waits for the air pressure switch to confirm adequate draught, signals the gas valve to open, and triggers the electrode spark. A fault anywhere on the board — or in the dedicated ignition transformer — can break this chain and produce a lockout without any single component being obviously failed.
How to fix it
- Check that other gas appliances in the property are working DIY safe
Turn on a gas hob ring or check a gas fire. If nothing else works, the problem is with your gas supply rather than the boiler. Contact your gas supplier or check whether a prepayment meter needs topping up. Do not attempt to reset the boiler until the supply is confirmed.
- Inspect the condensate pipe for freezing (cold weather only) DIY safe
Locate the white plastic pipe that exits the boiler and discharges outside or into an internal drain. In freezing conditions it may be blocked with ice. You can thaw it carefully by pouring warm (not boiling) water along its length or wrapping it with a warm damp cloth. Once clear, reset the boiler.
- Reset the boiler once or twice DIY safe
Press and hold the reset button as described in your user manual (typically 3–5 seconds). Allow the boiler a full start attempt before deciding it has failed again. If it locks out immediately on two resets, stop — repeated resets will not fix the underlying fault and could introduce unburnt gas into the flue system.
- Check system pressure is within range DIY safe
Look at the pressure gauge on the boiler. For most Remeha models the cold-fill pressure should sit between 1.0 and 1.5 bar. If it is below 0.8 bar, top up using the filling loop beneath the boiler until the gauge reads around 1.2 bar, then attempt a reset. Low pressure alone is unlikely to cause E.04.01 but is worth eliminating.
- Arrange a Gas Safe registered engineer visit for diagnosis Gas Safe engineer
If the fault persists after the checks above, a qualified engineer is required. They will inspect and test the ignition electrode and ionisation probe for wear, contamination, or misalignment — cleaning or replacing them as needed. They will also verify gas inlet pressure at the boiler, check the gas valve operation, inspect combustion seals and flue connections for leaks, test the air pressure switch and fan, and carry out a full flue gas analysis. Do not remove the boiler casing or touch any internal components yourself.
- Allow the engineer to replace faulty components Gas Safe engineer
The most common repair is a new ignition electrode or ionisation probe, both relatively straightforward replacements. If the gas valve or PCB is at fault the engineer will source the correct Remeha-compatible part — the PCB in particular may need to be ordered, leaving the boiler out of service for several working days. All gas-side work and PCB replacement must be performed by a Gas Safe registered engineer; doing it yourself is illegal and voids any remaining warranty.
Parts you may need
- Ignition electrode · from £45
- Ionisation probe / flame sensor · from £35
- Gas valve · from £120
- Combustion fan · from £130
- PCB / 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 £180–£400, depending on the underlying cause.
Frequently asked questions
Can I keep resetting the boiler to get it working while I wait for an engineer?
One or two resets is fine to confirm the fault is persistent, but do not keep cycling through resets after that. Each failed ignition attempt introduces a small amount of unburnt gas into the system, and the lockout is specifically designed to prevent that from accumulating. If the boiler will not stay lit after two resets, leave it off and call an engineer promptly.
How much does it typically cost to fix a Remeha E.04.01 fault in the UK?
Most homeowners pay somewhere between £180 and £400 all-in, depending on which component is at fault. An ignition electrode or ionisation probe replacement — the most common fix — usually falls at the lower end once you include the call-out, labour, and part. A gas valve replacement sits in the middle of that range. PCB replacement is the exception: parts alone can run to £280–£400 or more on top of labour, which is why it is worth getting a repair-versus-replace assessment if your boiler is over 12 years old and the PCB is the culprit.
Why does my Remeha keep showing E.04.01 every winter?
Recurring winter lockouts often point to a frozen condensate pipe. The condensate discharge pipe runs outside (or through an unheated space) and can ice up when temperatures drop below freezing. Insulating the external section of the pipe with foam lagging is an inexpensive fix that prevents repeat freeze-ups. If the fault appears in winter but the condensate pipe is clear, ask your engineer to check combustion seals — cold thermal cycling can cause seal shrinkage that worsens each winter.
Does annual boiler servicing reduce the risk of E.04.01 appearing?
Yes, meaningfully so. During a service the engineer will clean or replace the ignition electrode and ionisation probe before they degrade to the point of causing a lockout, check gas inlet pressure, inspect combustion seals, and clear any deposits from the burner. Catching electrode wear early is the single biggest preventive measure against flame-failure faults, and it also keeps the boiler running efficiently throughout the heating season.