Overview
E100 on a Baxi EcoBlue means the boiler has detected an internal clock/time error on the printed circuit board (PCB). The PCB contains a real-time clock or timing parameter storage that the boiler uses for timed functions and internal logging; if that clock or its memory is corrupted, the boiler will report E100. This error is usually related to the PCB electronics rather than to gas, water flow or the heat exchanger. Severity is generally low to medium. If the error is purely a clock/storage fault the boiler may still fire for heating and hot water under manual control, but timed programs, frost protection, or other time-dependent functions may be incorrect or disabled. However, an internal clock fault can also be a symptom of wider PCB or power-supply issues (for example following power spikes, intermittent mains, failed PSU components or water ingress), and those can eventually cause more serious faults or lockouts if left uninvestigated. Because the fault is electronic, DIY options are limited to safe checks and resets. If basic resets and checks do not clear the error, or if the boiler locks out, shows additional fault codes, or you smell gas, a Gas Safe registered engineer or Baxi-authorised service technician should be called—do not attempt PCB repair or replacement yourself unless you are a qualified heating engineer with electrical certification.
Possible Cause: Internal clock time error on printed circuit board (PCB)
Troubleshooting Steps
Safety precautions:
- If you smell gas, evacuate the property and contact the gas emergency service immediately. Do not operate switches, the boiler or any electrical devices.
- Isolate the boiler power at the external isolator before touching the boiler cover or any internal components. Only a qualified engineer should remove covers or work on gas and PCB components.
- Do not keep pressing reset repeatedly if the fault returns immediately; repeated resets can stress components and mask underlying issues.
Initial homeowner checks (safe, non-intrusive):
1. Note the exact code and any other codes or LEDs displayed. Take a photo of the display and note the date/time the fault appeared.
2. Check for recent power interruptions, lightning strikes, or tripped consumer unit (fuse box) that coincide with the fault appearing.
3. If you use a separate programmer/room thermostat with batteries, replace the batteries and confirm the programmer is set correctly. A faulty external timer can sometimes make the boiler report timing issues.
4. Check for obvious signs of water ingress or corrosion on the outside of the boiler case and around any flues or condensate outlets. Do not open the case.
Basic reset and restart steps (homeowner safe):
1. Try a standard reset: press and hold the boiler reset button as per the manual (usually 5–10 seconds) and watch the display for changes.
2. If reset does not clear the code, switch the boiler off at the mains isolator, leave it off for 1–2 minutes, then switch it back on and allow the boiler to reboot. Check the display again.
3. If the error clears and the boiler returns to normal operation, monitor it for recurrence. If E100 returns intermittently, record times and any events (power cuts, storms) that preceded it.
If the fault persists after reset and power-cycle: diagnostic information to gather before calling a pro
- Record model and serial number from the boiler rating plate.
- Write down the exact error code(s), any flashing LED patterns and whether the boiler is locked out or still operating.
- Note whether timed programs or the clock display on the boiler or programmer is wrong or blank.
What a qualified engineer will check (do not attempt unless qualified):
- Inspect the PCB for signs of physical damage, corrosion, water ingress or burned components.
- Check the boiler mains supply voltage and transient protection; verify the PSU/capacitor/back-up battery (if fitted) that supports the real-time clock and parameter storage.
- Run manufacturer diagnostics to read stored fault history and confirm whether parameter storage (PSU), EEPROM or RTC has failed or become corrupted.
- Reprogram or replace the PSU/PCB or replace faulty components if necessary, and restore parameters from backups if available. They will also check for root causes such as unstable mains, lightning damage, or moisture.
When to call a professional now:
- If the E100 code does not clear with reset and power-cycle.
- If additional fault codes appear, the boiler is locked out, or heating/hot water are unavailable.
- If you see signs of water damage, burning smell, or other electrical issues.
- If the boiler is under warranty or you prefer an authorised Baxi technician to preserve warranty and ensure correct PCB programming.
Final notes:
- Document everything (photos, times, events) before the engineer attends; it helps diagnosis.
- Do not attempt to replace or repair the PCB yourself unless you are a Gas Safe registered engineer with relevant electrical experience. PCB replacement and reprogramming should be done by a qualified technician.
- If the boiler is still providing heating/hot water in manual mode, you can continue to use it cautiously while you arrange a service visit, but monitor for further faults or loss of function.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi EcoBlue.