Remeha A.02.37 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha A.02.37 fault code mean?
The A.02.37 warning code appears when Remeha's eSMART control system detects that a non-safety-critical accessory on its internal CAN bus communication network has gone missing. The display on a Gas 220 Ace may show the text 'Uncritic device lost'. The 'uncritical' label is significant: the missing device is a peripheral — typically an SCB (System Control Board) expansion module, a zone controller, or a remote control accessory — rather than a core safety component. Because the boiler can still fire and operate without it, A.02.37 is a warning rather than a lockout. You may notice reduced functionality (for example, zone control or remote scheduling no longer responding), but heating and hot water will usually continue. The root cause recorded in Remeha's own service documentation is 'SCB not found', pointing to either a poor wiring connection to the accessory or a failure of the accessory board itself.
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
- Loose or disconnected wiring connector Common
The plug or connector linking the SCB expansion module (or other CAN bus accessory) to the boiler's main control board has vibrated loose, been accidentally dislodged, or was not fully seated during installation. This is the single most common trigger for A.02.37 and can sometimes be resolved simply by reseating the connector firmly.
- Corroded or damaged wiring loom Sometimes
If the connector has been exposed to moisture — common in older installations or boilers in damp utility cupboards — the terminals can corrode enough to break the CAN bus signal without the plug physically falling out. Chafed or pinched wiring can cause the same intermittent loss of communication.
- Failed SCB expansion board Sometimes
The System Control Board accessory itself may have suffered an electronic failure. If the wiring checks out but the boiler's control system still cannot detect the device after a rescan, the SCB board will need to be replaced.
- Accessory not detected after installation or reconfiguration Rare
If an SCB module or zone controller was recently added, moved, or the boiler's eSMART control was reset or updated, the controller may not have registered the accessory during its CAN bus scan. Running the auto-detect routine from the service menu is required to re-register it.
How to fix it
- Check whether the boiler is still providing heating and hot water DIY safe
Because A.02.37 is a warning rather than a lockout, the boiler often continues to run normally. Confirm whether your heating zones and hot water are working. If the boiler has shut down completely, there may be an additional fault code present — note any other codes showing on the display.
- Try resetting the boiler DIY safe
Press and hold the boiler's reset button for approximately 5 seconds, then release. Allow the boiler a minute or two to restart. If a connector was only slightly loose, a reset following step 3 below may be enough to clear the code. Do not reset more than 2–3 times in total without an engineer attending.
- Visually inspect accessible wiring connections to any external accessories DIY safe
If you can safely see the wiring between an external accessory (such as a wall-mounted zone controller or remote module) and the boiler without opening the boiler casing, check whether any plug or cable looks visibly loose, disconnected, or damaged. Do not open the boiler casing or touch any internal components — this step is limited to externally visible connections only.
- Have an engineer inspect and reseat all CAN bus wiring and connectors Gas Safe engineer
A Gas Safe registered engineer should open the boiler casing and methodically check every connector on the CAN bus wiring loom — looking for loose plugs, corroded terminals, and damaged cables. Reseating or replacing a connector is often all that is needed and can be completed within a single call-out.
- Run the eSMART auto-detect routine via the service menu Gas Safe engineer
The boiler's service menu (engineer access only) includes an auto-detect function that forces the eSMART controller to rescan for all connected CAN bus devices. This is particularly important if an SCB module was recently installed or if the control system has been reset. Only a trained Remeha engineer or Gas Safe registered engineer familiar with eSMART controls should carry this out.
- Test and, if necessary, replace the SCB expansion board Gas Safe engineer
If the wiring is intact and the auto-detect still fails to find the device, the engineer should test the SCB board directly. A confirmed faulty board will need to be replaced with the correct Remeha part for your model, and the eSMART system may require reconfiguration afterwards. This is not a homeowner task.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
If the above checks have not resolved A.02.37, or if you are in any doubt, book a visit from a Gas Safe registered engineer with Remeha experience. Explain that your boiler is showing A.02.37 so they can bring the appropriate diagnostic tools and, if needed, a replacement SCB module for your specific model.
Parts you may need
- Remeha SCB expansion board (System Control Board accessory) · from £120
- CAN bus wiring loom / connector harness · from £35
- eSMART controller interface module · from £95
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–£300, depending on the underlying cause.
Frequently asked questions
Will my boiler keep working while A.02.37 is showing?
In most cases, yes. A.02.37 is a warning code, not a lockout, so Remeha boilers typically continue to provide heating and hot water even while it is displayed. However, any function controlled by the missing accessory — such as multi-zone scheduling or a remote programmer — may stop working until the fault is resolved. You should still get the code investigated promptly, as ignoring communication faults can occasionally mask a worsening underlying issue.
What is an SCB and why does losing it trigger this code?
SCB stands for System Control Board — a plug-in expansion module that Remeha uses to add extra functionality to the boiler, such as additional heating zones, a hot water cylinder control, or integration with a smart thermostat system. The boiler communicates with the SCB over an internal CAN bus network. If the SCB disappears from that network (because its connector is loose or the board has failed), the eSMART control raises A.02.37 to alert you. Because the SCB is classed as a non-safety-critical accessory, the boiler keeps running — but it logs the warning.
How much does it cost to fix Remeha A.02.37 in the UK?
If the problem turns out to be nothing more than a loose connector, you are essentially paying for a call-out and the first hour of an engineer's time — typically £90–£150. If the SCB expansion board needs replacing, parts and labour together usually bring the total to around £200–£300. Prices are higher in London and the South East. In rare situations where the main eSMART controller is implicated, costs can be higher — your engineer can advise once they have diagnosed the exact cause.
Could A.02.37 come back after it has been cleared?
Yes, if the underlying cause was not fully addressed. A connector that was simply pushed back in without cleaning corroded terminals is likely to work loose again. An SCB board that is intermittently failing may also cause the code to reappear. If you see A.02.37 return within a few weeks of a repair, ask the engineer to check the connector condition more thoroughly or to test the SCB board under load. Regular annual servicing is the best way to catch deteriorating connections before they trigger fault codes.