Remeha E5 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha E5 fault code mean?
The E5 fault code on Remeha boilers — most commonly seen on the Avanta and Avanta Plus — indicates that the boiler has attempted to ignite and establish a stable flame but has failed to confirm one through its ionisation sensing system. Specifically, the boiler made five or more unsuccessful attempts to detect a valid ionisation signal during a single heat demand before locking out for safety. The ionisation current needs to sit between 3 and 9 microAmperes for the boiler to accept the flame as stable; if that threshold is not consistently met, the boiler shuts down. This is a lockout fault, meaning the boiler will not restart automatically and must be reset — though a reset alone will rarely cure the underlying problem.
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
- Dirty or worn ignition/ionisation electrode Common
Over time the electrode tip accumulates carbon deposits or simply degrades, reducing its ability to pass the required ionisation current through the flame. This is one of the most common findings on Remeha Avanta boilers showing E5 and is addressed during a proper service by cleaning or replacing the electrode — typically supplied as part of a Remeha service kit.
- Burner gasket failure Common
The rubber gasket sealing the burner bar can crack or distort, especially if the boiler has not been serviced regularly. A failed gasket allows combustion gases to escape out of alignment, disrupting the flame shape so the ionisation electrode cannot read it correctly. Replacing the gasket is a relatively inexpensive fix and Remeha recommend it is changed approximately every two years as part of routine maintenance.
- CO₂ combustion ratio incorrectly set Common
The gas-to-air ratio on the gas block must be precisely calibrated. If the CO₂ percentage is too high or too low, combustion is unstable and the ionisation current falls outside the acceptable 3–9 µA range. An engineer needs to check this with combustion analysis equipment and adjust the gas block accordingly.
- Flue or air-supply problem causing flue gas recirculation Sometimes
A blocked, incorrectly fitted, or poorly positioned flue terminal can allow exhaust combustion gases to be drawn back into the air inlet. This contaminates the air-fuel mix, producing an erratic flame the ionisation system cannot reliably detect. Checks should include all flue joints, the terminal position, and whether any nearby vents or obstructions are redirecting the exhaust plume.
- Failed ignition transformer Sometimes
The ignition transformer is responsible for generating the high-voltage spark to light the burner. If it is degrading it may still spark inconsistently, meaning the flame never fully establishes and the ionisation reading is either absent or too weak. Experienced engineers often fit a new ignition transformer alongside the service kit parts when resolving a persistent E5.
- Empty condensate trap Sometimes
If the condensate trap inside the boiler runs dry — which can happen if the boiler has been off for a prolonged period or after certain servicing operations — combustion air can be drawn through the trap and disrupt the flame. Refilling or priming the trap is a straightforward fix during a service visit.
- Thermostat parameter setting mismatch Rare
A less obvious but documented cause: if a room thermostat with an anticipation resistor is connected to the boiler and parameter P5 has not been changed from 0 to 1 in the boiler's settings, spurious heat demands can cause repeated ignition cycling that ultimately triggers an E5 lockout. If the fault persists after all hardware has been inspected, an engineer should check the boiler's parameter configuration.
- Faulty PCB (printed circuit board) Rare
In a small number of cases, all combustion components check out correctly but the fault persists because the PCB itself is misreading or failing to process the ionisation signal. PCB replacement is an expensive last resort and should only be considered once electrodes, gasket, transformer, and combustion settings have all been verified or replaced.
How to fix it
- Check that your gas supply is working normally DIY safe
Turn on a gas hob or check another gas appliance in the property. If nothing works, there may be a supply interruption — contact your gas network operator (e.g. Cadent, SGN, or Northern Gas Networks). Do not attempt to work on any gas pipework yourself.
- Reset the boiler (once or twice only) DIY safe
Press and hold the reset button for a few seconds until the boiler attempts to restart. You can try this up to two or three times, but if E5 returns each time it is a clear sign the underlying fault has not been resolved. Repeated resets without a repair will not help and may mask the problem.
- Check the system pressure DIY safe
Look at the pressure gauge on the boiler front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 0.8 bar, top it up via the filling loop following the instructions in your boiler manual. Low pressure alone is unlikely to cause E5 but is worth ruling out.
- Book a Gas Safe registered engineer for a full combustion inspection Gas Safe engineer
A qualified engineer should carry out combustion analysis, check the ionisation current with a microAmmeter, inspect the electrode and burner gasket, verify the flue and air-inlet connections, and adjust the CO₂ setting on the gas block. On the Remeha Avanta, experienced engineers typically fit a service kit (which includes the electrode and related consumables) plus a new ignition transformer as a package, then re-commission with combustion analysis.
- Engineer to inspect and replace the burner gasket if needed Gas Safe engineer
The burner bar gasket is a common and inexpensive cause of E5. The engineer should remove the burner assembly, inspect the gasket for cracking or distortion, and replace it. Remeha recommend this is done approximately every two years regardless.
- Engineer to check thermostat parameter P5 if fault persists Gas Safe engineer
If the boiler is connected to a room thermostat that incorporates an anticipation resistor, the engineer should access the boiler's installer parameters and confirm that P5 is set to 1 rather than the default of 0. This is a documented cause of recurring E5 faults that is easily overlooked.
- Engineer to test or replace the ignition transformer and, as a last resort, the PCB Gas Safe engineer
If all combustion components and settings have been addressed but E5 continues to return, the ignition transformer output should be measured. A weak or inconsistent output confirms the transformer needs replacing. Should the transformer also prove sound, the PCB may be at fault and will need to be replaced by a qualified engineer.
Parts you may need
- Remeha Avanta ionisation/ignition electrode (service kit) · from £45
- Burner bar gasket · from £18
- Ignition transformer · from £85
- Gas valve · from £160
- 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–£380, depending on the underlying cause.
Frequently asked questions
Can I fix the Remeha E5 fault myself without calling an engineer?
Your only safe homeowner actions are to check the gas supply is on, try a reset once or twice, and verify the system pressure. Everything else — adjusting the gas block, replacing electrodes, checking the ignition transformer, or accessing boiler parameters — must be carried out by a Gas Safe registered engineer. Working on gas appliances without the correct registration is illegal and dangerous.
Will resetting the boiler clear the E5 fault permanently?
Almost certainly not. A reset gets the boiler running again temporarily, but if the underlying cause — a worn electrode, failed burner gasket, incorrect CO₂ setting, or similar — has not been fixed, the fault will return, often within the same heating cycle. Repeated resets without a proper repair can delay diagnosis and sometimes cause additional wear. Book an engineer rather than relying on resets.
How much does it typically cost to repair a Remeha E5 fault?
Most homeowners pay somewhere between £150 and £380 all-in, depending on which components need attention. A full service with a new electrode kit, burner gasket, and combustion re-commissioning tends to fall in the £150–£250 range. If the ignition transformer also needs replacing, add roughly £100–£150 to that. A gas valve replacement usually costs £200–£350 including labour. The PCB is the most expensive possibility — parts alone can reach £250–£300, with the total repair typically £350–£500 — but PCB replacement is a last resort and is worth mentioning to your engineer before agreeing to it.
Could the Remeha E5 fault be caused by my thermostat?
Yes, in some cases. If your room thermostat has an anticipation resistor built in, there is a documented parameter setting — P5 — inside the boiler that must be changed from 0 to 1 to suit that thermostat type. Without this change, the boiler can cycle in a way that repeatedly triggers ignition failures and ultimately an E5 lockout. If your boiler has had electrodes and a gasket replaced but E5 keeps returning, ask your engineer to check the P5 parameter.