E100 Boiler Fault Code: What It Means on Every Brand

The E100 fault code appears on 2 brands — Baxi and Daikin — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 2 brands use this code Meaning differs by brand

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What E100 means	Severity	DIY?
BBaxi	The E100 code on a Baxi boiler indicates that the boiler's printed circuit board (PCB) has detected an internal clock timing fault. Full guide →	Engineer may be needed	No
DDaikinshown as E1-00	The E1-00 code on a Daikin heat pump signals a fault with the outdoor unit's printed circuit board (PCB) — the control board that orchestrates the compressor, fan motor, and all other… Full guide →	Lockout — engineer likely	No

E100 brand by brand

Baxi E100

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.

Causes, fixes & costs for Baxi E100 → · All Baxi codes

Daikin E1-00

The E1-00 code on a Daikin heat pump signals a fault with the outdoor unit's printed circuit board (PCB) — the control board that orchestrates the compressor, fan motor, and all other outdoor-unit functions. When this board fails or loses reliable communication, the system locks out and will not run until the underlying problem has been identified and resolved. The sub-code 00 indicates a significant system-level fault rather than a minor sensor glitch, so the unit needs professional attention if a simple power cycle does not clear it.

Causes, fixes & costs for Daikin E1-00 → · All Daikin codes

Frequently asked questions

Is the E100 fault code the same on every boiler?

No. E100 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a E100 fault myself?

Not usually. On every brand listed, E100 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a E100 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. For heat pumps, an MCS or F-Gas qualified heat pump engineer. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.