Remeha E.04.20 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.04.20 fault code mean?
The E.04.20 code belongs to Remeha's E.04.xx ignition fault family and indicates that the boiler has exhausted all of its permitted ignition attempts without successfully establishing a stable flame. Rather than continuing to retry indefinitely, the boiler enters a hard lockout to prevent any unsafe build-up of unburnt gas. The E.04.xx suffix numbering helps engineers pinpoint the precise nature of the failure: E.04.20 specifically points to a persistent ignition lockout — meaning the control board has detected repeated ignition failures and shut the boiler down completely until the root cause is identified and a manual reset is performed. Other codes in the same family you may encounter include E.04.01 (no spark detected), E.04.10 (spark present but no flame established), and E.04.30 (flame detected but ionisation signal too weak to confirm stable combustion) — all are variations on the same ignition-failure theme and are handled by similar diagnostic steps.
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 ignition electrode or lead Common
The ignition electrode and its high-voltage lead are the most frequently implicated components in E.04.20 lockouts. A high-value resistor (typically around 1 MΩ) within the electrode circuit can fail open-circuit, preventing any spark from forming. Cracked electrode insulators, carbon tracking on the PCB tracks around the electrode connection, or a corroded lead can all produce the same result. The electrode tip may also be fouled or positioned incorrectly relative to the burner.
- Insufficient ionisation current Common
Even when the burner lights briefly, the boiler's ionisation circuit must measure a current of roughly 3–9 microamps through the flame to confirm stable combustion. If the ionisation electrode (which may be the same component as the ignition electrode on some models) is dirty, damaged, or poorly earthed, the signal falls below the minimum threshold and the control board registers a lockout. A weak or broken earth connection is a frequent culprit here.
- Frozen or blocked condensate pipe Common
During cold weather, the condensate pipe that carries acidic waste water away from the boiler can freeze solid, causing a back-pressure that prevents the boiler from firing. On some Remeha models this triggers an ignition-family lockout rather than a dedicated condensate code. This is one of the few causes a homeowner can safely address themselves.
- Gas supply interruption Common
If the gas meter or supply valve has been turned off, a prepayment meter has run out of credit, or other gas appliances in the property have also lost supply, the boiler will fail to ignite every time and lock out. Always check other gas appliances first before assuming a boiler component has failed.
- Flue or air supply obstruction Sometimes
A blocked or incorrectly assembled flue restricts the flow of combustion air into the burner and the removal of exhaust gases. Recirculation of flue gases back into the air intake — sometimes caused by nearby obstructions or a poorly routed flue — can also disrupt ignition. The fan's ability to establish the correct air-pressure differential before ignition is part of this same sequence.
- Worn burner gasket or combustion seal Sometimes
The rope-style gasket that seals the burner chamber deteriorates over time and should ideally be replaced every two years during servicing. A degraded seal allows combustion air to escape around the burner, altering the gas-to-air ratio and causing unreliable or failed ignition. Replacing this relatively inexpensive component resolves the fault in a notable proportion of cases.
- Faulty gas valve Sometimes
The control board sends a precisely timed electrical signal to open the gas valve at the start of each ignition sequence. If a relay on the PCB has failed, wiring to the valve is damaged, or the valve itself is sticking, gas may not reach the burner at all — or may arrive inconsistently. In rare failure modes a stuck-open valve can also produce a lockout as a safety response.
- PCB (printed circuit board) failure Rare
The PCB orchestrates the entire ignition sequence — fan pre-purge, spark timing, gas valve operation, and ionisation measurement. A failing PCB can mimic almost any other ignition fault, which is why engineers usually rule out all other components before condemning the board. PCB diagnosis and replacement must only be carried out by a Gas Safe registered engineer.
How to fix it
- Check whether other gas appliances in the property are working DIY safe
Turn on a gas hob burner or check another gas appliance. If nothing gas-powered works, the problem is with the gas supply rather than the boiler. Contact your gas supplier or check that your meter has credit if you are on a prepayment meter. Do not attempt to reset the boiler until gas supply is confirmed.
- In freezing weather, check and thaw the condensate pipe DIY safe
Locate the plastic condensate discharge pipe — usually a white or grey pipe exiting through an external wall or running to an outside drain. If it feels solid or you can hear ice, pour warm (not boiling) water over the frozen section or wrap it with a warm wet cloth until it flows freely. Once thawed, proceed to reset the boiler.
- Check and top up boiler system pressure if needed DIY safe
Look at the pressure gauge on the boiler. Remeha boilers typically require 1.0–1.5 bar when cold. If the needle is below 0.8 bar, use the filling loop (two small valves on the pipework beneath the boiler) to slowly add water until the gauge reads around 1.2 bar, then close both valves. Low pressure alone is unlikely to cause E.04.20 but is worth correcting before a reset.
- Reset the boiler (no more than two or three times) DIY safe
Press and hold the reset button — usually marked with a flame or reset symbol — for around three seconds, or follow the specific reset procedure in your model's user guide. Allow the boiler a full ignition cycle of about 60–90 seconds. If it fires and runs normally, monitor it over the next day or two. If it locks out again with the same code, stop resetting and call an engineer — repeated resets without fixing the root cause will not help and may mask important diagnostic information.
- Call a Gas Safe registered engineer to carry out a full ignition system inspection Gas Safe engineer
An engineer will verify gas pressure and flow at the gas valve inlet, inspect the ignition electrode and high-voltage lead for wear or tracking damage, measure the ionisation current in the flame (target 3–9 μA), check the integrity of the earth connection, and inspect the burner gasket for deterioration. They will also check the flue for obstructions and verify the fan is producing the correct air-pressure differential before ignition is attempted.
- Engineer to test and replace the ignition electrode, lead, or burner gasket as required Gas Safe engineer
If the electrode tip is worn, cracked, or fouled, it will be replaced. The high-voltage lead and any in-line resistors are checked for continuity. If the burner rope gasket is compressed or damaged, it is replaced at this point — this is a cost-effective fix that resolves a meaningful proportion of E.04.20 faults. The engineer will retest ignition and ionisation current after each change.
- Engineer to test the gas valve operation and wiring Gas Safe engineer
The engineer checks that the control board is sending the correct signal to the gas valve and that the valve is opening and closing as expected. Wiring connections are inspected for corrosion or looseness. A faulty gas valve will be replaced by a Gas Safe registered engineer using manufacturer-approved parts.
- Engineer to assess the PCB if all other components test satisfactory Gas Safe engineer
If the ignition electrode, lead, gasket, gas valve, and flue have all been checked and are functioning correctly, the PCB becomes the prime suspect. The engineer will carry out board-level diagnostics. Depending on the boiler's age and the cost of a new board, they may discuss whether repair or full boiler replacement represents better value.
Parts you may need
- Ignition electrode and lead assembly · from £55
- Burner rope gasket / combustion seal · from £18
- Gas valve · from £175
- Ionisation electrode (if separate from ignition electrode) · from £40
- PCB / control board (reconditioned) · from £155
- PCB / control board (new OEM) · from £230
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–£380, depending on the underlying cause.
Frequently asked questions
Can I reset a Remeha E.04.20 fault myself and will it clear it?
You can safely attempt a reset once or twice — press and hold the reset button for about three seconds and allow the boiler a full ignition cycle. If the boiler fires and stays on, the fault may have been a one-off caused by a momentary gas supply blip or a temporarily frozen condensate pipe. However, if the E.04.20 code returns after one or two resets, stop resetting and call a Gas Safe registered engineer. Repeated resets without fixing the underlying fault will not resolve the problem and can make diagnosis harder.
How much does it typically cost to fix a Remeha E.04.20 fault in the UK?
Most homeowners with this fault pay somewhere between £150 and £380 once parts and labour are included. A straightforward ignition electrode replacement with a call-out typically falls in the £150–£220 range, while a gas valve replacement sits towards the upper end at around £300–£380. Bear in mind that a diagnostic call-out alone usually costs £60–£100 before any parts are ordered. In the less common scenario where the PCB is the root cause, costs can rise to £450–£700 — if your boiler is over ten years old and needs a new board, it is worth getting a new boiler quote alongside the repair quote.
What is the difference between E.04.20 and other E.04.xx codes on Remeha boilers?
The E.04.xx family all relate to ignition failures, but the suffix gives engineers more detail. E.04.01 typically indicates no spark was detected, E.04.10 means a spark was produced but no flame was established, and E.04.30 suggests a flame appeared but the ionisation current was too weak to confirm stable combustion. E.04.20 is the persistent lockout variant — it means the boiler has run through its full sequence of ignition attempts multiple times and shut down hard. In practice, the same components (electrode, gasket, gas valve) are checked for all of these codes; the suffix simply helps the engineer prioritise where to look first.
My Remeha keeps coming back with E.04.20 after being repaired — why?
A recurring E.04.20 after a repair usually means either that the root cause was not fully resolved, or that there is a secondary fault. Common scenarios include: the burner gasket was not replaced at the same time as the electrode (they wear together), there is a marginal ionisation earth connection that was not tightened, or the PCB has an intermittent relay fault that was not apparent during the initial repair visit. Ask your engineer to measure the ionisation current in microamps with a meter while the boiler is running — a reading below 3 μA confirms the ionisation circuit is the ongoing issue even if a spark is now present.