Alpha E28 Fault Code
The E28 fault is Alpha's fan and air pressure switch lockout — the PCB cannot confirm that the fan is running correctly or that the air pressure switch has triggered, and prevents ignition as a flue safety measure.
What is the Alpha E28 fault code?
The Alpha E28 fault is triggered when the control board does not receive a confirmed signal from the air pressure switch (APS) within the expected time after the fan starts its proving sequence. The APS confirms that the fan is generating sufficient flue draught for combustion gases to escape safely before ignition is permitted. E28 prevents ignition if there is any doubt about flue clearance — a critical safety lockout. The fault can originate at the fan motor, the APS itself, the rubber hose connecting them, a blocked flue terminal, or a frozen condensate pipe in winter.
What causes the E28 fault?
The fan motor degrades over time, running too slowly to generate sufficient flue draught for the APS to trigger. A common fault on Alpha boilers over 6–8 years old.
A bird nest, debris accumulation, or partial obstruction at the flue terminal restricts airflow and trips E28 even if the fan is running correctly.
The APS diaphragm can crack or the contacts can fail, showing E28 even when the fan is generating correct flue pressure.
A cracked or loose rubber hose between the APS and fan assembly prevents the APS from detecting fan pressure, triggering a false E28.
In cold weather, a frozen condensate pipe creates backpressure in the flue gas path, mimicking a blocked flue and triggering E28. Common in winter across South London.
A blocked condensate trap creates similar backpressure to a frozen pipe and can trigger E28 year-round if debris accumulates in the trap.
What you can safely check yourself
If safely visible from ground level, inspect the external flue terminal for obvious blockages — bird nests, leaves, or debris. Do not reach inside the flue terminal.
If the fault appears in cold weather, pour warm (not boiling) water over the external condensate pipe to thaw any ice blockage, then attempt one reset.
Hold the reset button for 3 seconds. Listen for the fan starting within 5 seconds. If E28 returns immediately, call a Gas Safe engineer — do not continue resetting.
Do not reset the boiler more than once if the fault code returns immediately. Repeated resets without diagnosis can mask a worsening fault.
What needs a Gas Safe engineer
- Test fan motor speed, current draw, and tachometer output
- Inspect the flue terminal and flue run for blockages or damage
- Test air pressure switch diaphragm integrity and contact operation
- Inspect the APS rubber hose for cracks, splits, or loose connections
- Clear or replace a blocked condensate trap
- Check PCB fan sensing circuit if all physical components test correctly
- Replace fan motor if speed is below specification
Fan and APS faults are common across South London's older housing stock. Many properties in Wandsworth, Merton, Lewisham, Lambeth, Southwark, Greenwich, and Bromley run Alpha boilers 6–12 years old — within the fan motor wear window. Frozen condensate pipes causing false E28 faults are a regular winter callout across South London, particularly in properties with externally routed condensate pipes.
How much does a E28 repair cost?
Costs below are UK averages. Reion provides a fixed quote after the £80 diagnostic visit — no obligation to proceed.
How to reset a Alpha boiler showing E28
In winter, check and thaw the condensate pipe before resetting.
Check the external flue terminal for visible blockages.
Hold the reset button for 3 seconds.
Listen for the fan starting within 5 seconds of pressing reset.
If E28 returns, do not reset again — call a Gas Safe engineer.
Fan replacement on Alpha boilers costs £200–£360 including parts and labour. Parts availability for Alpha fans can occasionally take 3–5 days versus next-day for Vaillant and Worcester Bosch. On a boiler under 8 years old, fan replacement is unambiguously worth doing. On an older Alpha with additional age-related concerns, Reion will give a comparison at the diagnostic visit.
Common questions about the Alpha E28 fault
What does Alpha E28 fault code mean?
Can I fix an Alpha E28 fault myself?
Why does my Alpha boiler show E28 in cold weather?
How much does an Alpha E28 repair cost in London?
Is an Alpha E28 fault dangerous?
Other Alpha fault codes
Need a Alpha engineer in London?
Reion is Gas Safe registered (919881), based in South London, and available 24/7. Fixed price after the diagnostic visit — no hidden charges.
