Alpha E24 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha E24 fault code mean?
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.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or seized fan motor Common
The fan motor is the most common culprit. Over time, the motor's bearings wear out or the windings burn out, causing the fan to stop spinning or run too slowly. The PCB detects the absence of the expected signal and locks the boiler out. Loft-installed boilers are particularly prone due to dust and debris ingress slowing the impeller.
- Loose or disconnected fan wiring Common
Constant vibration from normal boiler operation gradually loosens the electrical connections between the fan and the PCB. A loose plug, corroded terminal, or chafed cable can interrupt the fan's speed signal even when the fan motor itself is still serviceable.
- Blocked or obstructed flue Sometimes
A bird's nest, debris, or ice at the flue terminal can restrict the exhaust path enough to trigger an air pressure fault. This is more likely after storms, in autumn when leaves accumulate, or if the flue terminal is low to the ground or near vegetation.
- PCB misreading fan signals Sometimes
The printed circuit board may fail to correctly interpret the tachometer signal from the fan, even when the fan itself is working. Moisture ingress — not uncommon in UK boiler cupboards — can cause relay or component failure on the PCB, leading to a spurious E24 reading.
- Fan running below required speed Sometimes
A worn but not fully seized fan may spin at insufficient RPM. The boiler's air pressure system expects a minimum draught; if the fan is too slow, the pressure switch does not close and the lockout is triggered. Dust-clogged blades can also reduce airflow without the motor having fully failed.
How to fix it
- Check that the gas supply to your property is on DIY safe
Confirm other gas appliances such as your hob or gas fire are working. If there is no gas supply to the property, contact your gas supplier. A boiler fault caused by a temporary gas interruption can sometimes trigger secondary lockout codes including fan-related ones.
- Inspect the external flue terminal for obvious obstructions DIY safe
Go outside and visually inspect the flue outlet — usually a white or grey plastic terminal on an external wall or through a roof. Look for bird nests, leaves, ice, or anything physically blocking the opening. Do not insert anything into the flue. If you find a clear obstruction that can be safely removed without touching the flue pipe itself, do so, then proceed to reset.
- Reset the boiler once DIY safe
Turn the boiler off and allow it to sit for five minutes. Then press and hold the reset button on the control panel for approximately five seconds until the display changes. If the boiler fires up and runs normally, monitor it over the next hour. If E24 returns, do not continue resetting — repeated resets without fixing the underlying fault can cause further damage and mask a safety issue. Move on to calling an engineer.
- Gas Safe engineer: inspect and test fan wiring and connections Gas Safe engineer
An engineer will isolate power to the boiler and systematically check the fan's electrical connections — at the fan body, along the loom, and at the PCB — using a continuity tester to identify any open circuits, corroded terminals, or damaged insulation. Loose connectors are re-seated with insulated terminals and any damaged wiring sections are replaced.
- Gas Safe engineer: measure fan speed and assess the fan assembly Gas Safe engineer
Using the boiler's diagnostic or commissioning mode, the engineer will verify whether the fan is reaching the correct RPM. If the blades are clogged with dust or debris, they will be cleaned and the test repeated. If the fan motor is seized, running below specification, or drawing excessive current, the entire fan assembly will need to be replaced with a model-specific Alpha part to ensure correct airflow calibration.
- Gas Safe engineer: assess the PCB if wiring and fan are serviceable Gas Safe engineer
If the fan and all wiring check out correctly but the fault persists, attention turns to the PCB. The relay responsible for reading fan signals is a known failure point and can sometimes be repaired rather than replacing the whole board, which is a cost-effective option your engineer may offer. A full PCB replacement is the fallback if the board is beyond repair.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
If the boiler has not responded to a single reset and the flue is clear, there is nothing further a homeowner can safely do. The root cause — whether fan motor, wiring, or PCB — requires diagnosis and repair by a Gas Safe registered engineer. Always ask to see their Gas Safe ID card before work begins. You can verify registration at gassaferegister.co.uk.
Parts you may need
- Alpha fan assembly (model-specific) · from £115
- Fan wiring loom / connector kit · from £18
- PCB relay (repair component) · from £8
- Alpha PCB (full replacement, model-dependent) · from £220
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£380, depending on the underlying cause.
Frequently asked questions
Is it safe to keep resetting an Alpha boiler showing E24?
No. A single reset is reasonable to rule out a one-off glitch, but if E24 returns after resetting, the boiler is telling you there is a real fault that needs investigation. Repeatedly resetting it could cause further wear to the fan motor or, more importantly, could mask a flue obstruction that prevents combustion gases from safely leaving your home. If it locks out again, stop resetting and call a Gas Safe engineer.
How much does it cost to fix an Alpha E24 fault in the UK?
Most homeowners pay between £150 and £380 all-in for an E24 repair, covering the callout, labour, and parts. A loose wire re-connection at the lower end, or a fan replacement (fan parts typically £100–£120, plus an hour or two of labour) sits in the middle. PCB repairs — where just the faulty relay is replaced rather than the whole board — can keep costs down considerably. A full PCB replacement is the more expensive scenario and can push costs higher, but this is less common than a fan or wiring fix.
My Alpha boiler has LED lights flashing instead of an E24 code — is it the same fault?
Yes, on some older Alpha models that use LED indicators rather than a digital display, a fan or flue fault shows as the A and B indicator lights flashing simultaneously. This is the LED equivalent of the E24 family of faults and should be diagnosed in the same way — external flue check, one reset attempt, then a Gas Safe engineer if it persists.
Could the E24 fault mean my boiler needs replacing rather than repairing?
Not necessarily — fan and wiring faults are among the more straightforward boiler repairs. However, if your Alpha boiler is over 10–12 years old and the repair estimate is approaching £400 or more, it is worth getting a quote for a new boiler installation at the same time. A rough rule of thumb is that if the repair costs more than half the price of a comparable new boiler, replacement is likely better value in the long run. Your engineer should be able to advise honestly on the condition of the rest of the boiler.
Is the Alpha E24 fault covered under warranty?
If your Alpha boiler is still within its manufacturer warranty period and you have kept up with annual services as required by the warranty terms, contact Alpha directly before arranging an independent engineer. Alpha should be able to dispatch an authorised engineer to diagnose and resolve the fault at no cost to you. Arranging your own repair first may invalidate the remaining warranty cover.