Remeha A.02.18 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha A.02.18 fault code mean?
The A.02.18 is a warning-level code on Remeha Ace-series boilers. The display shows an Object Dictionary (OBD) Error, which means the boiler's electronic control system has detected that its internal configuration data — the stored set of parameters that tells the control board how the boiler should behave and communicate with its components — is either corrupted or incorrect. Unlike a full lockout, the boiler may continue running when this warning first appears, but the underlying cause needs prompt attention because warnings can escalate into a blocking fault or a full lockout if left unresolved. Resolving this code requires an engineer to re-synchronise the control board's configuration, which is not something a homeowner can safely do.
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
- Incorrect CN1/CN2 configuration values on the control board Common
Every Remeha Ace-series boiler has a pair of identification codes — CN1 and CN2 — printed on its data plate. If these values are not correctly stored in the control board (for example after a power interruption or a component swap), the system can no longer verify its own configuration, triggering the OBD error. This is one of the most direct causes listed in Remeha's own service documentation.
- Recent PCB or system control board replacement Common
Fitting a new PCB or system control board (SCB) without completing the correct commissioning steps — including running the auto-detect routine and re-entering the CN1/CN2 values — will often leave the object dictionary in an incomplete or mismatched state. The boiler raises A.02.18 because the new board has not yet been properly matched to the appliance.
- Corrupted firmware or parameter data Sometimes
The boiler's e-Smart microprocessor stores all operating parameters internally. A power surge, voltage spike, or interrupted firmware update can corrupt this stored data, causing a mismatch between what the control board expects and what it finds. The result is an OBD error even on hardware that is physically undamaged.
- SCB not detected by the main control unit Sometimes
If the system control board loses communication with the main controller — due to a loose connector, a failed board, or wiring damage — the main unit cannot populate its object dictionary correctly and raises this warning. The auto-detect routine is specifically designed to address this scenario.
How to fix it
- Check whether the boiler is still operating DIY safe
Because A.02.18 is a warning rather than a lockout, the boiler may still be producing heat and hot water. Note whether heating and hot water are working normally, and write down the exact code shown on the display. This information will be useful for your engineer.
- Attempt a single boiler reset DIY safe
Press the reset button as described in your boiler's user guide. If the warning clears and does not return within a short period, monitor the boiler closely over the next few hours. If the code reappears — which is likely with an OBD error — do not keep resetting, as repeated resets will not address the underlying configuration fault.
- Do not attempt to access the control board or internal settings Gas Safe engineer
The CN1/CN2 values, auto-detect routines, and parameter menus are engineer-level functions that require specialist knowledge of Remeha's service software. Accessing them incorrectly can deepen the configuration mismatch and potentially cause a full lockout. This work must only be carried out by a qualified heating engineer familiar with Remeha Ace-series boilers.
- Have a Gas Safe engineer run the auto-detect procedure Gas Safe engineer
Remeha's own service documentation specifies that when the SCB is not found or the object dictionary is in error, the engineer should carry out an auto-detect routine. This allows the control system to re-identify its connected boards and rebuild the object dictionary. The engineer will also verify the CN1 and CN2 values against the data plate on the boiler casing and re-enter them if necessary.
- Re-enter CN1/CN2 values and reset the system Gas Safe engineer
After the auto-detect, the engineer will confirm that the correct configuration codes are stored and perform a controlled reset. If the fault had escalated to a blocking state, the boiler should restart automatically once the cause is rectified; a lockout requires a manual reset after the fault is cleared.
- Replace the SCB or PCB if configuration steps do not resolve the fault Gas Safe engineer
If the auto-detect and parameter re-entry fail to clear the OBD error, the control board itself may be faulty. The engineer may need to consult Remeha's technical support team (Heateam) before ordering a replacement board, as Remeha can sometimes assist with remote diagnosis. A new PCB will need to be correctly commissioned before the boiler is returned to service.
- Contact a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Because A.02.18 is entirely an electronics and configuration fault, there are no further homeowner checks that will resolve it. Book a visit from a Gas Safe registered engineer who has experience with Remeha Ace-series boilers. Have the boiler's model number and serial number ready, along with the exact fault code, to help the engineer prepare.
Parts you may need
- Remeha Ace-series PCB / System Control Board (SCB) · from £280
- Boiler control unit ribbon cable / connector harness · from £35
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 £90–£350, depending on the underlying cause.
Frequently asked questions
Can I still use my boiler while the A.02.18 warning is showing?
In many cases, yes — A.02.18 is classified as a warning, which means the boiler may continue to operate. However, warnings on Remeha boilers can escalate into a blocking fault or a full lockout, so you should not ignore the code. Keep an eye on whether your heating and hot water continue to work normally and arrange an engineer visit promptly rather than waiting for a breakdown.
How much does it cost to fix a Remeha A.02.18 fault in the UK?
If the fault is resolved by an engineer running the auto-detect routine and re-entering the CN1/CN2 configuration values, you are typically looking at a standard call-out and labour charge — usually £90 to £150 depending on your location and the engineer's rates. If the PCB or system control board needs replacing, the all-in cost including parts and labour is typically £350 to £600, with the job taking one to three hours. In rare cases where a specialist Remeha board is required, costs can exceed this range, but a good engineer will discuss your options — including whether boiler replacement makes more financial sense if the appliance is over ten years old.
Why has A.02.18 appeared after my PCB was just replaced?
This is one of the most common triggers for the OBD error. When a new PCB or system control board is fitted, it needs to be commissioned correctly — this involves running the auto-detect routine so the new board can identify all connected components, and re-entering the CN1 and CN2 configuration codes from the boiler's data plate. If these steps were not completed, the object dictionary will be incomplete and the warning will appear. Contact the engineer who carried out the replacement and ask them to complete the commissioning procedure.
What are the CN1 and CN2 values and where do I find them?
CN1 and CN2 are a pair of identification codes that tell the Remeha control board exactly which boiler model and configuration it is managing. They are printed on the data plate, which is usually found inside the boiler casing or on the back panel. You do not need to do anything with these values yourself — your engineer will read them from the data plate and enter them into the control board's settings as part of fixing the A.02.18 fault.