H.01-.05 Boiler Fault Code: What It Means on Every Brand

The H.01-.05 fault code appears on 2 brands — Baxi and Remeha — 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 H.01-.05 means	Severity	DIY?
BBaxi	On Baxi boilers, H-series codes are 'blocking' faults — the boiler pauses or partially shuts down to protect itself but may resume automatically once the underlying condition clears. Full guide →	Engineer may be needed	Some checks
RRemehashown as H.01.05	The H.01.05 code appears on Remeha boilers — including the Tzerra Ace and Quinta Ace series that use the dot-notation fault code system — when the boiler detects an unusually large gap… Full guide →	Lockout — engineer likely	Some checks

H.01-.05 brand by brand

Baxi H.01-.05

On Baxi boilers, H-series codes are 'blocking' faults — the boiler pauses or partially shuts down to protect itself but may resume automatically once the underlying condition clears. They sit between a normal status message and a full lockout (E-code). The three defined groups are H.01 (circulation and temperature problems), H.02 (configuration, pressure and PCB issues), and H.03 (flue, flame and power supply faults). H.04 and H.05 do not appear in Baxi's published fault-code documentation; if your display shows either of those, consult your model's manual or call a Gas Safe engineer. Key sub-codes to look for: H.01.05 (flow-to-return temperature gap too large), H.01.08 (flow temperature rising too fast in heating mode — boiler pauses ~10 minutes), H.01.14 (maximum flow or return temperature reached), H.01.18 (temporary loss of water circulation), H.01.21 (flow temperature rising too fast during hot water production), H.02.07 (low system pressure — permanent condition), H.02.09 (partial shutdown, antifreeze active), H.02.10 (total shutdown, antifreeze not active), H.03.02 (temporary flame loss), H.03.05 (mains voltage too low), and H.03.54 (flame loss caused by low voltage).

Causes, fixes & costs for Baxi H.01-.05 → · All Baxi codes

Remeha H.01.05

The H.01.05 code appears on Remeha boilers — including the Tzerra Ace and Quinta Ace series that use the dot-notation fault code system — when the boiler detects an unusually large gap between the temperature of water leaving the heat exchanger (the flow) and the temperature of water coming back to it (the return). In a healthy system, this difference should be modest; when it becomes too wide, it usually means hot water is not moving around the system efficiently. The boiler responds by shutting down as a protective measure to avoid overheating internal components. The root cause is almost always a circulation problem, though a faulty temperature sensor giving a false reading can also trigger the code.

Causes, fixes & costs for Remeha H.01.05 → · All Remeha codes

Frequently asked questions

Is the H.01-.05 fault code the same on every boiler?

No. H.01-.05 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 H.01-.05 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a H.01-.05 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.