Alpha E50 Fault Code
The E50 fault is Alpha's ignition lockout — the boiler attempted multiple ignition sequences but could not establish or confirm a stable flame. It is the most common Alpha fault requiring a Gas Safe engineer, equivalent to Vaillant F.28, Worcester Bosch E1, and Baxi E168.
What is the Alpha E50 fault code?
The Alpha E50 fault is triggered when the PCB initiates a series of ignition attempts and the ionisation probe does not confirm a stable flame within the permitted window. Alpha boilers on E-Tec Plus and Evoke models typically make three attempts before displaying E50 and locking out. The fault can originate at any point in the ignition chain — gas supply, ignition electrode, ignition lead, gas valve, or ionisation probe — and requires a Gas Safe engineer to diagnose safely.
What causes the E50 fault?
A closed meter valve, empty prepayment meter, or work on the local gas network starves the boiler of gas. Always test another gas appliance before calling an engineer for E50.
The ceramic insulator cracks or the electrode tip corrodes over time, preventing a consistent spark from reaching the burner. A common cause on Alpha boilers that have not had annual servicing.
Combustion deposits on the probe prevent it detecting the flame. The PCB receives no flame signal and locks out — even if ignition was momentarily successful.
Cracked insulation on the high-voltage lead causes the spark to arc to ground. The electrode never receives the spark needed to ignite the gas.
A partially blocked or slow-opening gas valve provides insufficient gas at the burner during the ignition window. The spark fires but the flame cannot establish.
Dust, debris, or carbon deposits in the burner ports prevent even gas flow, resulting in partial or no ignition. More common on older Alpha units with missed servicing.
What you can safely check yourself
Turn on a gas hob or fire. If nothing works, the supply is the problem — call your gas supplier or check your prepayment meter before calling an engineer.
Ensure the emergency control valve at the meter is fully open (handle in line with the pipe). If it was accidentally knocked, open it fully and attempt one reset.
Hold the reset button for 3 seconds. Allow up to 60 seconds for the ignition sequence to complete. If E50 returns, do not reset again — call a Gas Safe engineer.
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 ignition electrode spark output and replace if degraded or cracked
- Clean or replace the ionisation probe to restore flame detection
- Inspect and replace the ignition lead if insulation is cracked or arcing
- Measure gas inlet pressure and manifold pressure at the burner
- Test gas valve opening speed and replace if response is sluggish
- Clean the burner if carbon deposits are restricting gas flow
- Check flue for backpressure that could prevent ignition
Hard water in South London — Wandsworth, Merton, Lewisham, Lambeth, Southwark, Greenwich, and Bromley — accelerates combustion deposits on the ionisation probe and burner. The calcium-heavy Thames Water supply contributes to burner fouling on Alpha boilers that miss annual services. E50 is the most frequently booked Alpha fault across Reion's South London callouts.
How much does a E50 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 E50
Confirm gas supply is working by testing another gas appliance.
Check the meter emergency control valve is fully open.
Hold the reset button for 3 seconds.
Wait for the full ignition sequence — up to 60 seconds.
If E50 returns, do not reset again. Call a Gas Safe engineer.
Gas valve replacement is among the more expensive Alpha repairs — typically £260–£420 all in. On an Alpha boiler under 8 years old in otherwise good condition, it is worth doing. On a boiler over 10 years old with parts availability concerns, Reion will give a clear repair-vs-replace comparison. Some Alpha gas valve parts take 3–5 days to source, which is a practical factor in the assessment.
Common questions about the Alpha E50 fault
What does an Alpha E50 fault code mean?
Can an Alpha E50 fault clear itself?
How long does an Alpha E50 repair take in London?
Is the Alpha E50 fault the same as a gas leak?
Why does my Alpha E50 fault keep coming back?
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.
