Error code
Baxi Boiler E78 — Code Meaning
The cited DUO-TEC table describes the lower limit of maximum gas-valve voltage; the calibration section includes E78 among possible incorrect-calibration indications. Only a qualified engineer should investigate. Only for the DUOTEC COMPACT, LUNA DUO-TEC, LUNA DUO-TEC MAX and NUVOLA DUO-TEC families (including the listed + versions) covered by Baxi Czech service manual dated 15 February 2018, pages 18–19. UK boilers and later versions require their own manual.
Quick answer
E78: Gas-valve calibration voltage-limit warning
Meaning
Gas-valve calibration voltage-limit warning
First safe check
Photograph the full display, including alternating characters and suffixes.
Stop if
The warning remains, the appliance is not operating normally, or the next step requires internal access.
Who to call
Contact a Gas Safe registered engineer qualified for this boiler if the warning remains, the code is not explained in the matching manual, or any internal investigation is required.
Internal diagnosis and repair require a qualified professional. Follow only the model-approved user actions described below. Keep checks outside the casing and use only a manufacturer-approved reset where the manual allows it.
What does this error code mean?
The cited DUO-TEC table describes the lower limit of maximum gas-valve voltage; the calibration section includes E78 among possible incorrect-calibration indications. Only a qualified engineer should investigate.
Only for the DUOTEC COMPACT, LUNA DUO-TEC, LUNA DUO-TEC MAX and NUVOLA DUO-TEC families (including the listed + versions) covered by Baxi Czech service manual dated 15 February 2018, pages 18–19. UK boilers and later versions require their own manual.
The reported condition does not, by itself, establish which part needs replacement.
Why is this happening?
- The manufacturer describes: gas-valve calibration voltage-limit warning. The underlying cause requires assessment on the actual model.
Safe next steps
- Photograph the full display, including alternating characters and suffixes.
- Record the full model from accessible paperwork or an external label; do not dismantle the appliance to find it.
- Match the source below to your exact model manual before following any code-specific instructions.
- If the warning persists, the model is uncertain or the next step requires internal access, stop and contact a Gas Safe registered engineer qualified for this boiler.
Can I fix this myself?
NoUse only the external checks described here. The code alone does not justify a parts replacement.
Safety boundary: Do not remove the boiler casing or work on gas, flue components, combustion settings or internal wiring.
What not to do
- Do not remove the boiler casing or work on gas, flue components, combustion settings or internal wiring.
- Do not repeatedly reset an unexplained or returning warning, or buy parts solely from this display.
When to call a heating professional
Contact a Gas Safe registered engineer qualified for this boiler if the warning remains, the code is not explained in the matching manual, or any internal investigation is required.
Safety warning
Do not remove the boiler casing or work on gas, flue components, combustion settings or internal wiring.
Useful hub links
Other Baxi boiler codes
Relevant guide
Frequently asked questions
Does E78 identify a failed part?+
No. A code describes a reported condition, and the correct model documentation is needed before diagnosis.
Does this apply to every model?+
Only for the DUOTEC COMPACT, LUNA DUO-TEC, LUNA DUO-TEC MAX and NUVOLA DUO-TEC families (including the listed + versions) covered by Baxi Czech service manual dated 15 February 2018, pages 18–19. UK boilers and later versions require their own manual.
Sources and review status
Model dependent · Last reviewed 21 September 2026
- Baxi Czech DUO-TEC service manual, 15 February 2018, pages 18–19
model manual · EU · checked 21 September 2026
Gas-valve calibration voltage-limit warning. Only for the DUOTEC COMPACT, LUNA DUO-TEC, LUNA DUO-TEC MAX and NUVOLA DUO-TEC families (including the listed + versions) covered by Baxi Czech service manual dated 15 February 2018, pages 18–19. UK boilers and later versions require their own manual.