H.03-.01 Boiler Fault Code: What It Means on Every Brand

The H.03-.01 fault code appears on 2 boiler brands — Baxi and Remeha — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Engineer may be needed 2 brands use this code

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 H.03-.01 means	Severity	DIY?
BBaxi	The H.03-.01 code is a temporary fault on Baxi boilers indicating that the main control board has lost communication with the HMI (Human Machine Interface) PCB — the front-panel display… Full guide →	Engineer may be needed	No
RRemehashown as H.03.01	H.03.01 is a blocking fault on Remeha ACE-series boilers, meaning the boiler has temporarily suspended operation rather than locking out permanently. Full guide →	Engineer may be needed	No

H.03-.01 brand by brand

Baxi H.03-.01

The H.03-.01 code is a temporary fault on Baxi boilers indicating that the main control board has lost communication with the HMI (Human Machine Interface) PCB — the front-panel display and user interface board. Because it carries the 'H.' prefix it is classed as temporary rather than a permanent lockout, which means a reset can sometimes clear it without further intervention. That said, if the underlying communication link between the HMI and the main PCB is genuinely broken — whether due to a loose connector, a damaged wiring harness, or a failed board — the fault will keep returning until the root cause is properly addressed.

Causes, fixes & costs for Baxi H.03-.01 → · All Baxi codes

Remeha H.03.01

H.03.01 is a blocking fault on Remeha ACE-series boilers, meaning the boiler has temporarily suspended operation rather than locking out permanently. It indicates that the main control unit (CU-GH) — the boiler's primary circuit board — has lost communication with the Gas Valve Controller (GVC), a dedicated sub-board that manages gas valve operation and safety functions. Because these two components can no longer exchange data, the boiler shuts down as a precaution. Unlike an E-code (permanent lockout), an H-code blocking fault means the boiler may be able to restart once the underlying issue is resolved or clears on its own.

Causes, fixes & costs for Remeha H.03.01 → · All Remeha codes

Frequently asked questions

Is the H.03-.01 fault code the same on every boiler?

Broadly, yes — on Baxi and Remeha the H.03-.01 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a H.03-.01 fault myself?

Not usually. On every brand listed, H.03-.01 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 H.03-.01 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. 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.