Protherm E6 Fault Code: Causes, Fixes & Repair Costs
What does the Protherm E6 fault code mean?
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.
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
- Gas supply interrupted or unavailable Common
If no gas is reaching the boiler, it simply cannot ignite. This could be a closed isolation valve, a prepayment meter that has run out of credit, or a wider supply interruption from your gas network operator. Try lighting a gas hob — if that also fails, the problem is with the supply rather than the boiler itself.
- Dirty or worn ignition and flame-sensing electrodes Common
Over time, electrodes accumulate carbon deposits or become corroded, making it difficult for the spark to jump reliably or for the sensor to confirm a flame is present. Even a small gap that has shifted out of specification can cause repeated ignition failures. This is one of the most frequently identified causes of E6 on Protherm boilers.
- Carbon build-up on the burner Common
Incomplete combustion gradually deposits soot on the burner surface, restricting gas flow through the burner ports. This leads to an uneven or weak flame that the ionisation electrode cannot reliably detect, triggering lockout.
- Gas valve not opening correctly Sometimes
The gas valve meters fuel into the combustion chamber. If it is mechanically worn, electrically faulty, or has incorrect pressure settings, insufficient gas will reach the burner and ignition will fail. Valve faults can develop gradually, causing intermittent E6 before becoming a permanent lockout.
- Flue or ventilation blockage Sometimes
A restricted or blocked flue prevents combustion gases from escaping safely. The boiler's safety systems detect the poor draught condition and shut down before or during ignition, which can manifest as an E6 lockout.
- Faulty ignition lead or wiring fault Sometimes
The high-voltage lead connecting the PCB to the ignition electrode can crack or degrade, causing the spark to be weak or absent. Poor earth connections and loose wiring at the electrode or gas valve can produce the same result.
- Fan failure or reduced fan speed Sometimes
The fan purges the combustion chamber before ignition and maintains the flue draught during firing. If the fan is running too slowly or not at all, the boiler's control board will typically prevent ignition — or the resulting poor draught will cause the flame to be unstable and trigger lockout.
- Faulty PCB (printed circuit board) Rare
The PCB manages the entire ignition sequence. A failed or damaged control board may not send the correct signal to the gas valve, the ignition transformer, or the fan — any of which can cause E6. PCB faults are less common but should be considered when all other components check out correctly.
How to fix it
- Check whether other gas appliances are working DIY safe
Go to your gas hob or another gas appliance and try to light it. If nothing gas-powered works, the fault is with your gas supply rather than the boiler. Contact your gas network operator (in the UK you can call the National Gas Emergency line on 0800 111 999 if you suspect a leak or total loss of supply) or check that your meter has not run out of credit.
- Confirm the gas isolation valve is open DIY safe
Locate the isolation valve on the gas supply pipe to the boiler — usually a quarter-turn lever near the appliance. It should be inline with the pipe (open). If it is at 90° to the pipe, it has been closed. Only open it if you know it was inadvertently shut; if you are unsure why it was closed, contact a Gas Safe engineer first.
- Check and top up the boiler's system pressure DIY safe
Look at the pressure gauge on the boiler. For most Protherm combi boilers, the correct cold pressure is between 1 and 1.5 bar. If it reads below 1 bar, use the filling loop to top up the system to around 1.2 bar. If the pressure is above 2.5 bar, do not attempt to fire the boiler and call an engineer. Low pressure alone is unlikely to cause E6 but eliminating it rules out a contributing issue.
- Attempt a boiler reset — once or twice only DIY safe
Press and hold the reset button (refer to your Protherm manual for the exact location on your model) for a few seconds until the boiler attempts to restart. Allow a full ignition cycle — this can take 30–60 seconds. If the boiler locks out again immediately, do not keep resetting. Repeated resets on a boiler that cannot establish a flame are unsafe and will not resolve the underlying fault.
- Inspect and clean or replace the ignition and flame-sensing electrodes Gas Safe engineer
A Gas Safe engineer will remove the burner cover, inspect both electrodes for carbon fouling, corrosion, or cracking, clean them thoroughly, check the gap is within the manufacturer's specification, and replace them if they are beyond serviceable condition. This is one of the most common and cost-effective fixes for E6.
- Clean or replace the burner Gas Safe engineer
The engineer will remove and inspect the burner for soot or debris blocking the ports. A thorough clean often restores correct gas distribution; badly fouled or damaged burners are replaced. This work requires access to sealed combustion components and must not be attempted by a homeowner.
- Test the gas valve operation and settings Gas Safe engineer
The engineer will check that the valve opens at the correct moment in the ignition sequence, verify gas inlet and outlet pressures against the boiler's specification, and test the electrical solenoid coils. A faulty or incorrectly set gas valve will be adjusted or replaced. All gas valve work requires Gas Safe registration.
- Inspect the flue and combustion air supply Gas Safe engineer
The engineer will check the flue terminal outdoors for blockages (bird nests, debris, ice), inspect the flue pipework for leaks or disconnection, and verify that combustion air can reach the appliance. A restricted flue is a safety-critical defect and must be resolved before the boiler is returned to service.
- Check the fan, ignition lead, and PCB Gas Safe engineer
If electrodes, burner, gas valve, and flue are all satisfactory, the engineer will measure fan speed and current draw, inspect the ignition lead for damage or tracking, and test the PCB outputs during the ignition sequence. Components found to be outside specification will be replaced.
- Call a Gas Safe registered engineer Gas Safe engineer
If the homeowner checks (gas supply, pressure, one or two resets) have not resolved the E6 fault, contact a Gas Safe registered engineer. You can verify any engineer's registration at gassaferegister.co.uk. Protherm's own guidance is clear that faults not cleared by a single reset require attention from a qualified specialist.
Parts you may need
- Ignition electrode (Protherm compatible) · from £25
- Flame-sensing / ionisation electrode · from £20
- Ignition lead / HT lead · from £18
- Gas valve (Protherm Emerald / Lynx compatible) · from £95
- Combustion fan · from £120
- PCB / control board · from £175
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 £100–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Protherm E6 fault myself?
Only very limited checks are safe for a homeowner: confirming the gas supply is on and other gas appliances work, checking system pressure and topping up if low, and attempting one or two resets. Every internal cause of E6 — electrodes, gas valve, burner, flue, fan, PCB — requires a Gas Safe registered engineer. Opening the boiler casing or touching gas components without the correct registration is illegal and dangerous.
How much will it cost to repair an E6 fault?
For the most common fixes, expect to pay roughly £100–£150 for electrode cleaning or replacement (parts and labour) and £180–£250 for a gas valve replacement including labour. A diagnostic callout from an independent Gas Safe engineer typically costs £60–£100 before any repair work. The total for a straightforward electrode or burner clean usually falls in the £100–£350 range. If a fan or PCB turns out to be faulty, costs can rise to £300–£500 or more; mention this to your engineer before authorising work so you can weigh the repair cost against the boiler's age and condition.
Why does my Protherm boiler show E6 but then fire up normally after a reset?
An intermittent E6 that clears on reset usually means a borderline fault — most often electrodes that are partially fouled or a gas valve that is slow to open — rather than a complete component failure. The boiler is telling you it struggled to light. Left unattended, intermittent faults almost always become permanent ones, so book a service or inspection sooner rather than later rather than relying on repeated resets.
My Protherm is a newer Panther or Gepard model — does E6 still apply?
On newer Protherm ranges (Panther, Gepard, and similar), fault codes are prefixed with 'F' rather than 'E'. Because the displays on some models only show two characters, the letter may not appear, making an F6 look like a bare '6' — which is easy to confuse with E6. Flame failure on those models is typically coded F6 or a similar variant. Always check your specific model's manual or data plate to confirm which code you are seeing, as the diagnostic steps and components involved can differ.