Boiler
128
Error code 128 on a Potterton boiler indicates a flame loss or ignition failure fault — the boiler is attempting to fire but cannot establish or maintain a stable flame. This is a lockout fault and your boiler will not produce heating or hot water until it is resolved.
What does this error mean?
When your Potterton boiler displays code 128, the boiler’s control board has detected that the burner either failed to ignite or the flame cut out unexpectedly during operation. The boiler locks itself out as a safety precaution to prevent unburned gas from accumulating. This is the boiler doing exactly what it should — but it does need attention before it will restart successfully.
Est. repair cost
£150–£300 for electrode/sensor repair; £300–£600 for gas valve or PCB replacement
🔍 Likely causes
🛠️ Step-by-step fix
Check your gas supply first: turn on a gas hob or check another gas appliance. If nothing works, call your gas supplier immediately — do not attempt a boiler reset.
Check for a frozen or blocked condensate pipe (common in winter). The condensate pipe is the plastic overflow pipe, usually running to an outside drain. If it’s frozen, carefully thaw it with warm (not boiling) water and a warm cloth.
Press the reset button on your Potterton boiler — typically a button with a flame or ‘reset’ symbol on the front panel. Hold it for 3–5 seconds as per your model’s manual. The boiler may attempt to re-ignite.
If the boiler fires but locks out again within a short period, do not keep resetting it repeatedly. More than two failed resets means an underlying fault needs diagnosing.
Check your boiler pressure gauge — it should read between 1 and 1.5 bar when cold. If it’s below 0.5 bar, top up via the filling loop following your manual. Low pressure alone won’t cause code 128, but it can contribute to ignition issues.
Beyond these steps, stop. Code 128 involves gas combustion components — all further diagnosis and repair must be carried out by a Gas Safe registered engineer.
📞 When to call a professional
If the boiler fails to fire after one or two resets, or immediately locks out again, call a Gas Safe registered engineer — do not keep resetting as this can indicate a gas valve or electrode fault that needs hands-on diagnosis. Tell the engineer: ‘My Potterton boiler is showing error code 128, it’s locking out on ignition failure.’ This helps them bring the right parts. If you smell gas at any point, do not reset the boiler — leave your home, leave doors open, and call the National Gas Emergency number on 0800 111 999 immediately.
⚖️ Repair or replace?
A Gas Safe engineer call-out with ignition electrode or flame sensor replacement typically costs £150–£300 in the UK, depending on your region and the engineer’s rates. If the fault lies with the gas valve or PCB, expect £300–£600 including parts and labour. If your Potterton boiler is over 10–12 years old and facing a repair above £400, replacing it with a modern A-rated combi boiler (typically £1,800–£3,000 installed) is usually the more cost-effective long-term choice.