Potterton E128 Fault Code: Causes, Fixes & Repair Costs
What does the Potterton E128 fault code mean?
The E128 code appears on Potterton boilers when the appliance has lost its flame — or failed to establish one — during normal operation. As a safety measure, the boiler will attempt to re-ignite automatically, but once it has made around 12 unsuccessful attempts it gives up and locks out, displaying E128 on the panel. The root cause is most commonly a problem with ignition components, gas supply, or a frozen condensate pipe in winter. On some Potterton models, particularly older Promax units, the fault can also reflect a PCB-level electrical failure rather than a straightforward ignition issue. Either way, the boiler will not restart safely until the underlying fault has been resolved.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- Frozen condensate pipe Common
In freezing weather, the plastic condensate pipe that runs outside the property can ice up, blocking the flow and causing the boiler to lock out. This is one of the most frequent reasons for E128 faults during winter. A gurgling noise when the boiler tries to fire is a classic giveaway.
- Gas supply interruption or low pressure Common
If the gas meter regulator has frozen, a nearby supply has been interrupted, or your utility provider is delivering gas at below-normal pressure, the boiler will struggle or fail to ignite repeatedly until E128 triggers. Check whether your gas hob or other gas appliances are working normally.
- Worn or fouled ignition electrode or lead Common
The ignition electrode and its lead are consumable components that degrade with use. A cracked ceramic insulator, carbon build-up on the probe tip, or a damaged lead will prevent the spark from reliably igniting the gas. This is a particularly common finding on older Profile and Suprima models.
- Faulty flame detection sensor Sometimes
Even when ignition occurs successfully, the boiler relies on a separate flame-sensing component to confirm the burner is alight. If this sensor is dirty, misaligned, or failing, the control board will not register a flame and will keep retrying until lockout.
- Gas valve fault Sometimes
A gas valve that is sticking, partially blocked, or failing to open fully will restrict gas flow to the burner, preventing reliable ignition. This requires a Gas Safe engineer to test and, if necessary, replace.
- PCB failure or electrical fault Rare
The printed circuit board governs ignition timing, flame sensing, and all safety checks. Component failure due to age, moisture ingress, or a power surge — particularly common on Promax models over ten years old — can cause the board to misread or fail to trigger ignition correctly, producing an E128 lockout even when all other components are in good condition.
How to fix it
- Check that other gas appliances are working DIY safe
Try your gas hob or fire. If nothing gas-powered works, there may be a supply interruption. Contact your gas supplier before doing anything further.
- Check for a frozen condensate pipe DIY safe
Look for the white or grey plastic pipe that exits the boiler casing and runs to an outside drain or gully. In cold weather, feel along its length for a hard, icy section. If you find one, gently pour warm (not boiling) water over the frozen area until the blockage clears. Do not use a blowtorch or very hot water, as this can crack the pipework.
- Reset the boiler DIY safe
Once any condensate blockage has been cleared (or if no blockage was found), press and hold the reset button on the boiler's control panel for three to five seconds. Allow the boiler a few minutes to attempt ignition. If it fires and stays on, monitor it over the next day or so. Do not reset more than two or three times in total — repeated failed resets will not fix an underlying fault and can mask important safety information.
- If the fault returns, call a Gas Safe registered engineer Gas Safe engineer
A qualified engineer will carry out a systematic diagnosis: testing the ignition electrode, lead, and spark generator for wear or damage; checking gas pressure at the appliance; inspecting the flame sensor for contamination or misalignment; testing the gas valve for correct operation; and evaluating the PCB outputs before deciding whether the board needs replacement. Do not attempt any of these checks yourself — working on gas components without Gas Safe registration is illegal and dangerous.
Parts you may need
- Ignition electrode · from £25
- Ignition lead / HT lead · from £20
- Flame sensing electrode · from £22
- Gas valve · from £120
- PCB (model-dependent, new or refurbished) · from £150
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 £120–£380, depending on the underlying cause.
Frequently asked questions
Can I reset a Potterton E128 fault myself?
Yes — a single reset is a sensible first step, and thawing a frozen condensate pipe before resetting is also something you can safely do. However, if the boiler locks out again with E128 after one or two resets, you should stop and call a Gas Safe engineer. Repeatedly resetting a boiler with a genuine ignition or gas-supply fault does not fix the problem and could be unsafe.
How much does it typically cost to fix a Potterton E128 fault in the UK?
Most homeowners pay somewhere between £120 and £380 including labour and parts, depending on what the engineer finds. A straightforward ignition electrode swap sits at the lower end of that range. A gas valve replacement will be higher. If the PCB turns out to be the culprit, the total cost for parts and labour on popular models such as the Promax or Performa can reach £400–£600, so it is worth asking your engineer to test individual board outputs before committing to that repair.
Why does my Potterton boiler keep showing E128 every winter?
Recurring winter lockouts strongly suggest a frozen condensate pipe. Many Potterton boilers have condensate pipes routed through unheated spaces or along exposed external walls where they are prone to icing. A Gas Safe engineer can reposition or insulate the pipe to prevent the problem repeating — a relatively inexpensive fix that saves repeated callouts.
My Potterton boiler is over 12 years old and showing E128 — is it worth repairing?
Potterton boilers typically have a service life of around 12 to 15 years. If yours is within that range and the fault is a minor ignition component, repair is usually worthwhile. If the PCB has failed on an older Profile or Suprima, parts availability can be limited and the repair cost may approach the price of a new, more efficient boiler. Ask your engineer for an honest assessment before authorising expensive work on an ageing appliance.