Baxi E78 Fault Code: What It Means and How to Fix It
If your Baxi boiler is showing the E78 fault code, it means there’s an issue with the water pressure sensor specifically, the boiler is unable to detect the correct system pressure. This can cause your boiler to shut down or work inefficiently, leaving you without heating or hot water.
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What Does the Baxi E78 Fault Code Mean?
The Baxi E78 Fault Code indicates a pressure sensor fault. Your boiler uses this sensor to monitor water pressure and ensure it’s within the correct operating range (typically between 1.0 and 1.5 bar). If the sensor is faulty or sends incorrect signals, your boiler may:
- Show the E78 error code
- Stop working
- Operate unsafely or inefficiently
This is a safety lockout feature to protect the boiler and your home.
Common Causes of the Baxi E78 Error Code
Several issues could trigger the E78 fault:
Faulty Pressure Sensor
The sensor itself may have failed and is no longer sending accurate pressure readings.
Loose or Damaged Wiring
The electrical connections between the sensor and the boiler’s control board could be loose, corroded, or broken.
System Blockages or Airlocks
A blockage in the system or air trapped in the pressure sensor line can cause false readings.
PCB (Printed Circuit Board) Issue
Rarely, the control board may not interpret the sensor’s signals correctly.
How to Fix the Baxi E78 Fault Code
Time needed: 5 minutes
Here’s a step-by-step overview of how a Gas Safe registered engineer would typically fix this fault:
- Check Boiler Pressure
Look at the pressure gauge. If pressure is below 1.0 bar, top it up using the filling loop to 1.2–1.5 bar.
- Reset the Boiler
Try resetting the boiler once the correct pressure is restored.
- Inspect Wiring Connections
A qualified engineer will check the wiring between the sensor and PCB for faults.
- Test and Replace Pressure Sensor
If wiring is intact, the engineer will test the pressure sensor and replace it if it’s not functioning properly.
- PCB Inspection
As a last resort, the PCB will be checked and replaced if needed.
When to Call a Gas Safe Engineer
If you’ve topped up your boiler pressure and the E78 error still shows, don’t attempt further DIY fixes. Call a Gas Safe engineer to safely:
- Test and replace the pressure sensor
- Repair wiring
- Reset system errors
- Check for hidden leaks or PCB faults
Final Thoughts
The Baxi E78 Fault Code may sound minor, but it’s your boiler’s way of preventing unsafe operation. In most cases, it’s a quick fix for a trained engineer but leaving it unresolved could cause your boiler to shut down or suffer long-term damage.
Frequently Asked Questions
To reset a hot water boiler, locate the reset button on the control panel. Press and hold the button for 10 seconds, then wait a minute to see if the system resumes normal operation. If the error persists, repeat the process.
If your Baxi boiler is showing the E55 fault code, it means there’s a communication issue between the boiler’s printed circuit board (PCB) and one of its connected components. Here is Baxi E55 error code guide.
