AL41 Boiler Fault Code: What It Means on Every Brand

The AL41 fault code appears on 2 brands — Sime and Vokera — 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 AL41 means	Severity	DIY?
SSimeshown as AL 41	The AL 41 code appears on Sime boilers when the burner flame has been lost six times in a row during the ignition sequence. Full guide →	Lockout — engineer likely	No
VVokera	The AL41 code (also shown simply as A41 on many Vokera displays — both refer to the same fault) is a transitional low-pressure warning. Full guide →	Engineer may be needed	Some checks

AL41 brand by brand

Sime AL 41

The AL 41 code appears on Sime boilers when the burner flame has been lost six times in a row during the ignition sequence. After this sixth consecutive failed attempt to establish and hold a flame, the boiler locks out entirely and displays AL 41 to protect itself from further damage. This is a safety lockout — the boiler will not restart automatically and requires manual intervention. The root cause can range from a straightforward gas supply issue to a faulty component within the ignition or burner system, so the fault needs to be investigated carefully before simply resetting the boiler repeatedly.

Causes, fixes & costs for Sime AL 41 → · All Sime codes

Vokera AL41

The AL41 code (also shown simply as A41 on many Vokera displays — both refer to the same fault) is a transitional low-pressure warning. It triggers when the system water pressure drops below 0.3 bar, which the boiler considers unsafe for continued operation. Vokera gives the boiler a 10-minute window to allow you to act; if the pressure is still too low after that period, the code upgrades to A40, which is a full lockout. Think of A41 as an early alert — the boiler is telling you the system needs water before it shuts down completely. In rare cases, a faulty pressure sensor can also cause A41 to appear even when actual system pressure is normal, because the boiler cannot read the pressure correctly.

Causes, fixes & costs for Vokera AL41 → · All Vokera codes

Frequently asked questions

Is the AL41 fault code the same on every boiler?

No. AL41 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 AL41 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a AL41 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.