E24 Boiler Fault Code: What It Means on Every Brand

The E24 fault code appears on 4 boiler brands — Alpha, Biasi, Keston 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 4 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 E24 means	Severity	DIY?
AAlpha	The E24 fault code on Alpha boilers indicates a problem within the fan, flue, or combustion air pressure circuit. Full guide →	Lockout — engineer likely	No
BBiasi	The E24 code on a Biasi boiler has two distinct meanings depending on which model range you own. Full guide →	Lockout — engineer likely	No
KKeston	The E24 code appears on Keston boilers — most notably the C36 — when the system water pressure has dropped enough to require topping up on four or more occasions within a single 24-hour… Full guide →	Lockout — engineer likely	No
RRavenheat	The E24 code on a Ravenheat boiler indicates a fault with the heating return NTC thermistor — the small temperature-sensing component clipped or screwed onto the return pipework inside the… Full guide →	Lockout — engineer likely	No

E24 brand by brand

Alpha E24

The E24 fault code on Alpha boilers indicates a problem within the fan, flue, or combustion air pressure circuit. The boiler's control board monitors the fan before allowing ignition — if it fails to detect the fan running correctly, or if airflow through the flue system is compromised, the boiler locks out and displays E24. This protects against unburnt gases accumulating inside the heat exchanger. On older Alpha models with LED indicators rather than a digital display, an equivalent signal appears as the A and B indicators flashing simultaneously, pointing to the same fan or flue fault. The code belongs to Alpha's E20-series fault family, which covers fan, flue draught, and combustion air issues across the Intec, E-Tec, CD, and related ranges. Note: if your specific Alpha model shows a variation such as E20, E21, or E23, those also fall within this fan-flue family — check your model's manual for the precise sub-meaning, but the diagnostic approach is broadly the same.

Causes, fixes & costs for Alpha E24 → · All Alpha codes

Biasi E24

The E24 code on a Biasi boiler has two distinct meanings depending on which model range you own. On newer Biasi models (such as the Rinnova), E24 signals a probable flue or chimney obstruction — the control board has detected that combustion gases are not being safely expelled and has locked the boiler out as a precaution. On older Biasi models (such as the Riva and 24S ranges), E24 indicates incorrect burner operation during ignition — the burner failed to establish properly when the boiler attempted to fire. In both cases the boiler will not operate until the underlying fault is resolved. Check your model handbook if you are unsure which definition applies; the troubleshooting approach overlaps significantly either way.

Causes, fixes & costs for Biasi E24 → · All Biasi codes

Keston E24

The E24 code appears on Keston boilers — most notably the C36 — when the system water pressure has dropped enough to require topping up on four or more occasions within a single 24-hour period. Rather than flagging a one-off pressure dip, the boiler's control board is telling you it has noticed a recurring pattern of pressure loss, which strongly suggests water is escaping from somewhere in the system. When E24 triggers, the boiler locks out and will not restart until the Reset button is pressed. Simply re-pressurising and resetting may bring the boiler back temporarily, but the code will return unless the underlying cause — almost always a leak — is properly identified and fixed.

Causes, fixes & costs for Keston E24 → · All Keston codes

Ravenheat E24

The E24 code on a Ravenheat boiler indicates a fault with the heating return NTC thermistor — the small temperature-sensing component clipped or screwed onto the return pipework inside the boiler. This sensor monitors the temperature of water flowing back into the boiler from the central heating circuit. When the PCB receives a signal that is out of range, implausible, or missing entirely from this sensor, it cannot safely track the heating circuit's thermal state and will lock the boiler out as a precaution. In plain terms: the boiler's electronics have lost confidence in the return temperature reading and have shut down to prevent potential overheating.

Causes, fixes & costs for Ravenheat E24 → · All Ravenheat codes

Frequently asked questions

Is the E24 fault code the same on every boiler?

Broadly, yes — on Alpha, Biasi, Keston and Ravenheat the E24 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 E24 fault myself?

Not usually. On every brand listed, E24 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 E24 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.