E25 Boiler Fault Code: What It Means on Every Brand

The E25 fault code appears on 3 boiler brands — Alpha, Biasi and Ravenheat — 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.

Lockout — engineer likely 3 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 E25 means	Severity	DIY?
AAlpha	The E25 fault code on Alpha boilers is a protective shutdown triggered when the boiler attempts to fire but cannot confirm that water is flowing through the system. Full guide →	Lockout — engineer likely	Some checks
BBiasi	The E25 code appears on Biasi boilers — including the Binova and Rinnova ranges — when the boiler detects an insufficient or inconsistent gas supply during normal operation. Full guide →	Lockout — engineer likely	No
RRavenheat	The E25 code on a Ravenheat boiler indicates that the main heat exchanger has frozen. Full guide →	Lockout — engineer likely	Some checks

E25 brand by brand

Alpha E25

The E25 fault code on Alpha boilers is a protective shutdown triggered when the boiler attempts to fire but cannot confirm that water is flowing through the system. This is often called a 'dry fire' fault — the boiler's safety logic detects conditions consistent with running without adequate water, which could cause serious damage to internal components. The fault is most commonly traced to low system pressure or a faulty flow sensor, but blocked heat exchangers, trapped air, and in some cases a PCB fault (particularly noted on the Alpha E-Tec 28) can also trigger the same code. On some models, a temperature sensor or wiring fault may produce an E25 even when pressure is normal, so it is worth considering sensor issues if pressure checks out fine.

Causes, fixes & costs for Alpha E25 → · All Alpha codes

Biasi E25

The E25 code appears on Biasi boilers — including the Binova and Rinnova ranges — when the boiler detects an insufficient or inconsistent gas supply during normal operation. The boiler locks itself out as a safety precaution. Biasi's own guidance points to three areas to verify: that the gas connection is correct, that the flue outlet is clear and open, and that the gas pressure gauge (manometer) is functioning properly. Until the underlying cause is identified and resolved, the boiler will refuse to fire.

Causes, fixes & costs for Biasi E25 → · All Biasi codes

Ravenheat E25

The E25 code on a Ravenheat boiler indicates that the main heat exchanger has frozen. The heat exchanger is the component responsible for transferring heat from the burner flame into the water that circulates around your heating system. When it freezes — or when the boiler detects conditions severe enough to risk freezing — the boiler locks out to protect itself, leaving you without heating or hot water until the fault is cleared.

Causes, fixes & costs for Ravenheat E25 → · All Ravenheat codes

Frequently asked questions

Is the E25 fault code the same on every boiler?

Broadly, yes — on Alpha, Biasi and Ravenheat the E25 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 E25 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 E25 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.