Baxi E100 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E100 fault code mean?
The E100 code on a Baxi boiler indicates that the boiler's printed circuit board (PCB) has detected an internal clock timing fault. The PCB relies on its built-in clock for coordinating timing functions across the system, and when that clock behaves unexpectedly — whether due to a power event, a new board being fitted, or PCB deterioration — the boiler logs this error and may stop operating normally. While it sounds technical, the first step is always a simple reset, since the code can occasionally appear after a brief, harmless glitch. If the code persists, the PCB itself will need professional attention.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Power interruption or electrical surge Common
A sudden loss of mains power or a voltage spike can corrupt the PCB's internal clock, causing it to flag an E100 error on restart. This is particularly common after a power cut or if the boiler is on a circuit prone to fluctuations.
- Recently replaced or newly installed PCB Common
When a PCB is replaced or a brand-new boiler is commissioned, the replacement board's internal clock may not yet be synchronised to the boiler. This requires entering a product code from the boiler's manual to pair the PCB correctly. Without this step, E100 is a typical result.
- PCB wear or age-related degradation Sometimes
Over time, the electronic components that maintain the PCB clock can deteriorate — particularly if the boiler has been running hot, has been exposed to moisture from a nearby leak, or has simply reached the end of its serviceable life. Gradual wear can cause the clock to behave erratically.
- Faulty sensors or peripheral component interference Rare
On occasion, a sensor elsewhere in the boiler (such as a temperature or pressure sensor) that is sending corrupt signals can cause the PCB to log errors that appear clock-related. This is worth ruling out before committing to a full PCB replacement.
How to fix it
- Reset the boiler DIY safe
Locate the reset button on the front of your Baxi boiler — on most models it is a clearly marked button or a flame symbol. Press and hold it for around 1–3 seconds until the boiler restarts. Wait a few minutes to see if the E100 code clears. A one-off power glitch can leave a fault code displayed even after the underlying issue has resolved itself. Repeat the reset no more than two or three times in total; if the code keeps returning, move on to the next step.
- Check that the mains power supply and gas supply are normal DIY safe
Confirm that other appliances in the property are working normally, that no fuses have tripped, and that the gas supply is on (check another gas appliance such as a hob). A recent power cut or tripped circuit breaker could have triggered the clock fault and may clear once power is stable.
- If a PCB was recently fitted, synchronise it to the boiler DIY safe
If your boiler has just been installed or had its PCB replaced by an engineer, the new board will need pairing to the boiler using the product or configuration code found in your Baxi user manual. This is a menu-based process — follow the manual instructions carefully. If you are not confident doing this, ask the engineer who fitted the board to complete the commissioning step.
- Contact a Gas Safe registered engineer for diagnostics Gas Safe engineer
If the E100 code persists after resetting, or if no PCB work has recently been carried out, a Gas Safe engineer should inspect the boiler. They will check whether the PCB clock circuit is genuinely faulty, whether a sensor is sending corrupted data, or whether the board needs repair or full replacement. Do not attempt to open the boiler casing or handle the PCB yourself — this is not safe for a homeowner and could invalidate your warranty.
- PCB repair or replacement by a Gas Safe engineer Gas Safe engineer
Where the PCB is confirmed as faulty, the engineer will advise whether a repair is viable or a full replacement is needed. A replacement PCB must be correctly configured and commissioned before the boiler is returned to service. Ensure you ask the engineer to check whether the boiler is still within its Baxi warranty period, as parts and labour may be partially or fully covered.
Parts you may need
- Baxi PCB (replacement board, model-specific) · from £220
- Surge protection plug or device · from £25
- Boiler temperature sensor (if identified as contributing fault) · from £35
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£380, depending on the underlying cause.
Frequently asked questions
Can I fix the Baxi E100 fault myself?
The only homeowner-safe actions are resetting the boiler (up to two or three times) and, if a PCB has just been replaced, following the manual's synchronisation steps. Any further diagnosis or work on the PCB itself must be carried out by a Gas Safe registered engineer. Handling the PCB without the correct qualifications is unsafe and will likely void your warranty.
How much does it cost to fix a Baxi E100 error?
Most people with an E100 fault pay somewhere between £120 and £380, which typically covers the engineer's call-out, diagnostics, and any minor repair or re-commissioning work. If the PCB needs a full replacement, the total cost including parts and labour is usually in the region of £450–£700 — parts alone can run from around £180 to £400 depending on the specific Baxi model. London and the South East tend to sit at the top of these ranges.
Why has my Baxi boiler shown E100 after a power cut?
A power cut or voltage spike can disrupt the internal clock on the PCB, which is exactly what E100 flags. In many cases, a single reset after mains power is restored will clear the code and the boiler will run normally again. If the code keeps reappearing after the reset, the PCB may have sustained more lasting damage from the electrical event and will need a professional inspection.
Is it worth replacing the PCB on an older Baxi boiler?
If your boiler is relatively young — say, under eight to ten years old and otherwise in good condition — a PCB replacement can restore reliable operation for several more years. For older boilers, it is worth asking your engineer to assess the overall condition of the system first. As a rough guide, if the repair bill would exceed half the cost of a comparable new boiler, replacement often makes better long-term financial sense. A new Baxi boiler also comes with a manufacturer warranty of at least two years, extendable to up to ten years when fitted by a Baxi-accredited installer.