E99 error code
ACV HeatMaster 25 C EVO E99 error code – Control bus communication lost
What does ACV HeatMaster 25 C EVO combined boiler and water heater E99 mean?
ACV documents E99 for the HeatMaster 25 C EVO as “Control bus communication lost”. Communication between the appliance display and controller has been lost.
The code identifies the condition detected by the product; it does not always identify the failed component on its own. Confirm the full code and exact model before ordering parts or attempting a reset.
The ACV HeatMaster 25 C EVO combined boiler and water heater E99 error code indicates aCV documents E99 for the HeatMaster 25 C EVO as “Control bus communication lost”. Communication between the appliance display and controller has been lost. This guide explains what the code means, the symptoms and likely causes, the checks that are safe to make, and when to stop and arrange an authorised repair.
Symptoms you may notice
The HeatMaster 25 C EVO displays E99 and may suspend burner, heating or hot-water operation until the detected condition is corrected.
Common causes
Possible causes are those described by ACV for control bus communication lost, including the associated component, wiring, circulation, configuration or safety circuit.
Before you start troubleshooting
Use the display, rating label or product menu to confirm the exact model. Similar-looking codes can have different meanings across product generations and regions.
- Record the complete code before switching the equipment off.
- Check only user-accessible controls, filters and external connections described in the manual.
- Do not open gas, refrigerant, combustion or electrical compartments.
Troubleshooting steps
Check wiring between the display and controller. The appliance restarts when communication is restored.
Can you fix this error code yourself?
The safest next step depends on the exact model and the cause behind the code. External checks may help, but a returning fault needs professional diagnosis.
A successful reset is not proof that the underlying issue is fixed. If E99 reappears, note when it happens and give that information to the service engineer.
Reset instructions
Use only the reset or restart procedure described in the official HeatMaster 25 C EVO manual. Do not repeatedly reset a returning fault.
Applicable products and models
HeatMaster 25 C EVO combined boiler and water heaterHeatMaster 25 C EVO2024 onwardWhen to contact a professional
Contact an ACV-qualified heating engineer if the code returns, the appliance remains locked out, a safety device has operated, or checks require internal access, test equipment or replacement parts.
Frequently asked questions
What does ACV HeatMaster 25 C EVO combined boiler and water heater E99 mean?
ACV documents E99 for the HeatMaster 25 C EVO as “Control bus communication lost”. Communication between the appliance display and controller has been lost.
Can I fix ACV HeatMaster 25 C EVO combined boiler and water heater E99 myself?
Some external checks may be suitable for the user, but the result depends on the exact model and cause. Use the official manual and arrange service if the code returns.
Should I reset the product after code E99?
Use only the reset or restart procedure described in the official HeatMaster 25 C EVO manual. Do not repeatedly reset a returning fault.
When should I arrange a repair?
Contact an ACV-qualified heating engineer if the code returns, the appliance remains locked out, a safety device has operated, or checks require internal access, test equipment or replacement parts.