E6 Boiler Fault Code: What It Means on Every Brand

The E6 fault code appears on 3 boiler brands — Alpha, Protherm and Remeha — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Lockout — engineer likely 3 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What E6 means	Severity	DIY?
AAlpha	The E6 code on an Alpha boiler points to a fault with the central heating (CH) flow temperature sensor — an NTC thermistor that continuously measures the temperature of water leaving the… Full guide →	Lockout — engineer likely	No
PProtherm	The E6 code on a Protherm boiler signals that the appliance has attempted to light its burner but failed to establish or hold a stable flame, so it has shut itself down as a safety measure… Full guide →	Lockout — engineer likely	No
RRemeha	The E6 fault code on a Remeha boiler is a safety lockout triggered when the boiler's control system detects a flame signal during a period when no burner operation has been requested — in… Full guide →	Lockout — engineer likely	No

E6 brand by brand

Alpha E6

The E6 code on an Alpha boiler points to a fault with the central heating (CH) flow temperature sensor — an NTC thermistor that continuously measures the temperature of water leaving the heat exchanger. When the boiler's PCB detects that the signal from this sensor is outside expected parameters (either no signal, an erratic reading, or an implausibly high or low resistance value), it locks out and displays E6 to prevent unsafe operation. Note: E6 is not explicitly listed in every Alpha model's documentation. If your display shows a slightly different code, always cross-reference your model's manual or call Alpha's technical helpline, as code numbering can vary across the Intec, E-Tec, and CD-series ranges. The underlying cause — a temperature sensor or wiring issue — is broadly consistent across the range.

Causes, fixes & costs for Alpha E6 → · All Alpha codes

Protherm E6

The E6 code on a Protherm boiler signals that the appliance has attempted to light its burner but failed to establish or hold a stable flame, so it has shut itself down as a safety measure — a condition sometimes called ignition lockout. The boiler makes two or three ignition attempts; if it still cannot detect a flame, it stops trying and displays E6 to alert you. On Protherm's Emerald range, the same fault is indicated by the LED blinking once green followed by six red flashes. Note that on older, simpler Protherm ranges (such as the Emerald and Lynx), fault codes begin with 'E', whereas on newer models (Panther, Gepard, and similar), the equivalent codes are prefixed with 'F' — because those displays show only two characters, the 'F' prefix may not appear on screen. If your display shows what looks like '6' without a letter, check your model's manual to confirm you are reading E6 rather than F6.

Causes, fixes & costs for Protherm E6 → · All Protherm codes

Remeha E6

The E6 fault code on a Remeha boiler is a safety lockout triggered when the boiler's control system detects a flame signal during a period when no burner operation has been requested — in other words, the boiler thinks it can see a flame even though it has been told to stay off. Because an unexpected flame signal represents a potential safety hazard, the boiler shuts itself down and refuses to restart until the underlying cause is identified and resolved. The fault is most commonly traced back to a faulty PCB (printed circuit board) misreading or generating a spurious flame signal, although a contaminated or degraded ionisation/flame sensor can produce the same symptom. Until the root cause is fixed, any reset will only provide temporary relief.

Causes, fixes & costs for Remeha E6 → · All Remeha codes

Frequently asked questions

Is the E6 fault code the same on every boiler?

Broadly, yes — on Alpha, Protherm and Remeha the E6 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a E6 fault myself?

Not usually. On every brand listed, E6 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a E6 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.