Error code
Baxi Boiler Fault Code E78
Control board or internal communication fault The most likely cause is control board issue. Check first: do not keep resetting if the fault returns straight away.
Quick answer
E78: what does it mean and how to fix
What does it mean?
Control board or internal communication fault
How to fix first
Try one standard user reset if the manual permits it.
Why is this happening?
Control board issue
When should I call an engineer?
Persistent electronics and communication faults need a qualified heating engineer rather than further user troubleshooting.
What does this error code mean?
Baxi boiler fault code E78 usually means the boiler has detected an internal electronics or communication problem.
In practice, E78 is commonly linked to Control board issue, Loose or damaged internal wiring, or A connected component failing to respond correctly.
Start with this safe check: Try one standard user reset if the manual permits it. If the code returns, the fault worsens, or the appliance does not behave normally, persistent electronics and communication faults need a qualified heating engineer rather than further user troubleshooting.
Why is this happening?
- Control board issue
- Loose or damaged internal wiring
- A connected component failing to respond correctly
How to fix this safely
- Try one standard user reset if the manual permits it.
- Do not keep resetting if the fault returns straight away.
- Arrange professional diagnosis for persistent control faults.
Reset steps
- Use the normal user reset once only.
- Book an engineer if the boiler remains locked out.
When to call an engineer
Persistent electronics and communication faults need a qualified heating engineer rather than further user troubleshooting.
Safety warning
Do not remove the casing or attempt internal electrical repairs on the boiler.
Useful hub links
Related PCB and control fault codes
Relevant guide
Frequently asked questions
Can I keep resetting a Baxi boiler with E78?+
No. If E78 returns after one standard user reset, stop there and arrange a qualified engineer if the manual gives no safe next step.
Is E78 something I can repair myself?+
Boiler faults should be treated cautiously. Stay within the user checks in the manual, and leave gas, combustion, and internal boiler repairs to a qualified professional.