Critical Serial EEPROM Storage Failure Error Stop unit Manual Control Board failure, check lights
The A156 error code on Carrier boilers indicates critical serial eeprom storage failure error stop unit manual control board failure, check lights.
Carrier A156 means: critical serial eeprom storage failure error stop unit manual control board failure, check lights. The usual causes are problem has been detected with the eeprom storage on the, mbb. try resetting the power and check the indicator lights. if or the alarm continues, the board should be replaced. You can safely reset the boiler once — if A156 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does A156 Mean
The A156 code is shown by the boiler’s control board when it detects critical serial eeprom storage failure error stop unit manual control board failure, check lights. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows A156 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 1 technical sources.
| Cause |
|---|
| problem has been detected with the EEPROM storage on the |
| MBB. Try resetting the power and check the indicator lights. If |
| the alarm continues, the board should be replaced. |
Safety Warning
A156 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Check for visible damage on the PCB — look for burnt components, corrosion, or water marks
Check all wiring connections to the PCB are secure
Try a power cycle — switch the boiler off at the mains for 30 seconds, then switch back on
If the fault persists after power cycling, check the error code history for related faults
Verify the mains voltage supply to the PCB is stable (230V ±10%)
Check the earth connection
How to Fix It
Power cycle the boiler (off for 30 seconds, then on)
repair loose connections
if the PCB shows signs of water damage or burnt components, replace the PCB
ensure the replacement PCB is the correct version for the boiler model
after PCB replacement, the boiler may need recommissioning and parameter setup
Refer to the Carrier service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
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Affected Models
Carrier models that can display fault code A156:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Carrier models | — | Possible |
Frequently Asked Questions
Power cycle the boiler (off for 30 seconds, then on). According to the technical documentation, this is the first check on the list for A156.
A156 is not classified as a high-severity fault, so the boiler can be reset once. If A156 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.