Remeha E.04.05 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E.04.05 fault code mean?
The E.04.05 code belongs to Remeha's E4 fault family, which covers ignition and flame establishment failures. In plain terms, the boiler has attempted to light several times in succession — more than five start attempts — without successfully detecting a stable flame, so it has locked itself out as a safety measure. The sub-code .05 identifies the precise failure mode within that ignition category, pointing toward a problem with either the spark generation, the flame signal (ionisation current), or the gas reaching the burner at the right pressure. Until the underlying fault is resolved and the boiler is reset, it will not attempt to fire again. This is a deliberate safety lockout, not a random glitch.
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 damaged burner rope gasket Common
A small rope seal sits between the burner and the burner door. When this seal deteriorates, combustion gases can escape into the wrong area, causing ignition to occur away from the ionisation probe. The boiler fires but cannot detect its own flame, triggering the lockout. Engineers report this as one of the most frequently overlooked causes on Remeha boilers, and Remeha's own service kit includes a replacement gasket for this reason.
- Faulty or misaligned ignition electrode Common
The ignition electrode is responsible for both generating the spark and, in many Remeha designs, detecting the ionisation current once the flame is established. Over time, electrodes can bend out of position, corrode, or crack. The ionisation current must sit between roughly 3 and 9 microamperes — if the electrode is worn or mis-gapped, the signal falls below this threshold and the boiler locks out even when gas is present.
- Failing ignition transformer Common
The ignition transformer supplies the high-voltage spark to the electrode. If it begins to fail, the spark becomes too weak or intermittent to reliably ignite the gas mixture. Engineers note that after ruling out the rope gasket and electrode, the ignition transformer is the next most likely culprit. A 1 MΩ resistor within the detection circuit can also go open-circuit, which mimics a transformer fault and requires careful measurement at the PCB connector with the electrode lead disconnected.
- Gas supply or pressure problem Sometimes
If the gas pressure at the valve is outside the specified range, the burner will either receive too little gas to ignite or none at all. This can be caused by the main gas tap being partially closed, low network pressure, air in the supply line (common after pipework work), or an incorrect CO₂ calibration on the gas block. Other gas appliances in the property not working normally is a strong indicator of a supply issue.
- Flue gas recirculation Sometimes
If combustion products are being drawn back into the air intake — either due to a poorly sited flue terminal, blocked flue, or a damaged internal flue connection — the air-to-gas ratio is disrupted and reliable ignition becomes impossible. This cause is less obvious and requires the engineer to inspect both the external flue terminal position and the internal air-supply connections.
- PCB (printed circuit board) failure Rare
The PCB controls the entire ignition sequence and interprets the ionisation signal. If the board itself is faulty, it may fail to energise the transformer, misread the ionisation current, or abort the ignition sequence prematurely. PCB failure is a diagnosis of exclusion — engineers will exhaust all other possibilities first, as the board is the most expensive component involved.
How to fix it
- Check your wider gas supply DIY safe
Turn on another gas appliance in your home — a gas hob burner is ideal. If it lights normally, your gas supply is fine. If nothing gas-powered is working, the issue is with your supply rather than the boiler itself: contact your gas supplier or call the National Gas Emergency Service on 0800 111 999.
- Reset the boiler once or twice DIY safe
Switch the boiler off at its controls, wait around 30 seconds, then switch it back on. Many Remeha models have a dedicated reset button; consult your user manual for the exact procedure. Attempt this no more than two or three times in total. Repeated resets on a boiler that is locking out due to a genuine fault will not fix anything and can be unsafe — the boiler is shutting down for a reason.
- Check boiler system pressure DIY safe
Look at the pressure gauge on the boiler front. For most Remeha domestic boilers, the cold system pressure should sit between 1.0 and 1.5 bar. If it has dropped below 0.8 bar, top it up using the filling loop beneath the boiler following the instructions in your user manual. Low pressure alone is unlikely to cause E.04.05, but it is worth eliminating.
- Inspect the condensate pipe for freezing (winter months) DIY safe
In cold weather, the external condensate pipe can freeze and cause the boiler to lock out. Locate the plastic condensate pipe (usually white or grey, running outside through an external wall). You can carefully pour warm — not boiling — water over it to thaw it, then reset the boiler. Note: a frozen condensate pipe typically triggers a different fault code, but it is a quick check worth making before calling an engineer.
- Gas Safe engineer: inspect and test the burner rope gasket Gas Safe engineer
The engineer will remove the burner door to examine the condition of the rope seal around the burner assembly. A compressed, cracked, or hardened gasket should be replaced. Remeha produces a combustion chamber service kit that includes this gasket along with other wear items — many engineers fit the full kit at this point rather than replacing parts individually.
- Gas Safe engineer: test ignition electrode and ionisation circuit Gas Safe engineer
The engineer will measure the ionisation current (target: 3–9 µA) and inspect the electrode for correct positioning, cracking, or contamination. The 1 MΩ resistor in the detection lead should be tested for continuity with the electrode connection removed. The lead itself is checked from the electrode tip back to the PCB connector. A Remeha service kit typically includes a replacement electrode.
- Gas Safe engineer: check gas pressure and CO₂ calibration Gas Safe engineer
Working gas pressure at the valve inlet is verified at both high and low firing rates. The engineer will also check the CO₂ percentage in the flue at both rates and adjust the gas valve air-to-gas ratio if required. Incorrect combustion settings can prevent stable flame formation even when all components are intact.
- Gas Safe engineer: inspect flue and air supply connections Gas Safe engineer
The engineer will check all internal flue connections for integrity and inspect the external flue terminal for blockages or signs of recirculation. Any damaged seals or incorrect flue routing must be corrected before the boiler is returned to service.
- Gas Safe engineer: test or replace the ignition transformer Gas Safe engineer
If the rope gasket, electrode, and gas settings all check out satisfactorily, the engineer will test the ignition transformer output. A weak or intermittent output confirms the transformer has failed and needs replacing.
- Gas Safe engineer: diagnose and replace PCB if required Gas Safe engineer
Only once all other components have been eliminated should the PCB be considered. The engineer will carry out electrical tests on the board's ignition outputs. On a boiler that is more than 8–10 years old, the cost of a new PCB should be compared directly against the cost of a replacement boiler installation before committing to the repair.
Parts you may need
- Burner rope gasket / combustion chamber service kit · from £45
- Ignition and ionisation electrode · from £55
- Ignition transformer · from £90
- Gas valve · from £130
- 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 £100–£350, depending on the underlying cause.
Frequently asked questions
Can I fix Remeha E.04.05 myself by resetting the boiler?
A single reset is always worth trying — occasionally the lockout is caused by a one-off event such as a brief dip in gas pressure and the boiler will light normally afterwards. However, if it locks out again with the same code, repeated resetting will not resolve the fault and is not safe practice. The underlying cause needs to be diagnosed and fixed by a Gas Safe registered engineer.
What is the most common physical cause of E.04.05 on a Remeha boiler?
Based on engineer reports and trade forum discussions, the burner rope gasket is the single most frequently identified cause. When this seal deteriorates, gas ignites in the wrong location so the ionisation probe never sees a flame, even though combustion is technically occurring. A worn ignition electrode or failing ignition transformer are the next most common causes. Remeha's own service kit covers all three items, so engineers will often replace the full kit in a single visit.
How much does it typically cost to repair a Remeha E.04.05 fault?
For the most common repairs — replacing the burner rope gasket and electrode, or fitting a new ignition transformer — most homeowners pay between £100 and £350 including parts and labour. A gas valve replacement tends to sit toward the top of that range. A full PCB replacement is considerably more expensive, often £400–£650, and on a boiler over 10 years old it is worth comparing that cost against a new boiler before proceeding.
How can I prevent E.04.05 from happening again?
Annual servicing by a Gas Safe engineer is the most effective preventative measure. During a service, the engineer will inspect and replace worn ignition components, check gas pressure and combustion settings, and renew the burner rope gasket if needed. Catching component wear before it causes a complete lockout significantly reduces the chance of being left without heating or hot water, particularly in winter.