Protherm E7 Fault Code: Causes, Fixes & Repair Costs
What does the Protherm E7 fault code mean?
The E7 code (sometimes displayed as Eb on certain Protherm models) indicates that the boiler's control board has attempted to fire the burner but failed to detect a successful ignition. As a safety measure, the boiler locks out rather than continuing to try. The electronic control unit continuously monitors signals from key sensors, and when the ignition or flame signal is absent or falls outside the expected range, E7 is triggered. This is essentially the boiler telling you: 'I tried to light the burner, but something stopped it from working correctly.'
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
- Dirty or contaminated ignition electrodes Common
Carbon build-up, soot, or moisture on the ignition electrode or ionisation sensor is the most frequent trigger for E7. When these components are coated in residue, the spark either fails to generate or the boiler cannot confirm that a flame has been established, causing it to lock out.
- Worn or damaged ignition electrodes Common
Over time — typically every 3 to 5 years — ignition electrodes degrade through normal use. Cracking, corrosion, or physical wear means the electrode can no longer produce a reliable spark. Annual servicing should catch this, but missed services accelerate wear.
- Interrupted or low gas supply Common
If the gas supply to the boiler is restricted or cut off — perhaps because the gas isolation valve is partially closed, a prepayment meter has run out, or there is a supply issue from the network — the burner cannot light regardless of how good the ignition components are.
- Loose wiring or poor electrical connections Sometimes
Boiler vibration over months and years can gradually loosen wiring connections between the ignition electrodes, the spark generator, and the control board. Weak or intermittent electrical signals can mimic a component failure and trigger E7.
- Faulty gas valve Sometimes
A gas valve that is stuck closed, incorrectly calibrated, or failing will prevent gas from reaching the burner. Even when all ignition components are in good order, the flame cannot be established without adequate gas flow.
- Blocked or partially obstructed flue Sometimes
A restricted air intake or blocked flue — particularly from ice build-up on the flue terminal in cold weather — can disrupt the combustion conditions the boiler needs to achieve a stable ignition. The boiler may lock out on E7 as a result.
- Poor earthing of the boiler Rare
The ionisation flame detection system relies on a good electrical earth to function correctly. A faulty or inadequate earth connection can cause the boiler to misread the flame signal and trigger a spurious ignition lockout.
- Control board (PCB) failure Rare
If all other components check out correctly, the PCB itself may be faulty. A failing control board can send incorrect signals to the ignition system or fail to process the flame confirmation signal, resulting in E7 as a last resort diagnosis.
How to fix it
- Check that your gas supply is active DIY safe
Before anything else, confirm that other gas appliances in your home — such as a gas hob or a gas fire — are working normally. If they are not, contact your gas supplier. Also check that the gas isolation valve on the pipe feeding the boiler is fully open (handle in line with the pipe).
- Reset the boiler DIY safe
Press and hold the reset button on your Protherm boiler as described in your user manual — typically for around 3 seconds. Allow the boiler a full minute to attempt ignition. If E7 returns immediately, do not reset more than two or three times in quick succession, as repeated failed ignition attempts can indicate a real fault that needs investigation.
- Check whether the flue terminal is blocked or frozen DIY safe
Head outside and visually inspect the flue outlet on the external wall. In cold weather, ice can form and partially block the terminal. If you see ice, you can carefully pour warm (not boiling) water over it to thaw it. Do not use tools to chip at ice near the flue. If the flue looks clear, this is unlikely to be the cause.
- Have a Gas Safe engineer inspect and clean the ignition electrodes Gas Safe engineer
A registered engineer will access the burner chamber, remove the electrodes, and assess their condition. Light carbon deposits can often be gently cleaned; if the electrodes are cracked, corroded, or heavily fouled, replacement is straightforward and significantly cheaper than more involved repairs.
- Have the engineer check ignition wiring and connections Gas Safe engineer
Using a multimeter, the engineer will test the wiring between the electrodes, the spark generator, and the PCB. Loose or corroded connections are re-secured or replaced. This is a quick check that often resolves intermittent E7 faults at low cost.
- Have the gas valve tested and adjusted or replaced if necessary Gas Safe engineer
The engineer will verify the gas valve is opening correctly and that gas pressure at the burner meets the boiler's specification. A stuck valve can sometimes be freed and re-set; a faulty valve will need replacement.
- Have the boiler's earthing inspected Gas Safe engineer
The engineer should verify the boiler is correctly earthed to ensure the ionisation flame detection circuit operates reliably. Poor earthing can cause ghost faults that are difficult to diagnose without systematic checks.
- If all else fails, seek a PCB diagnosis Gas Safe engineer
A control board replacement is a last resort. If the engineer has confirmed that electrodes, wiring, gas valve, and earthing are all serviceable, the PCB may be the root cause. Given the cost of a PCB, ask the engineer to carry out thorough diagnostics before committing to this repair, and get a written quote.
Parts you may need
- Ignition electrode (single) · from £25
- Ionisation / flame sensing electrode · from £30
- Ignition lead set · from £35
- Spark generator / ignition transformer · from £65
- Gas valve · from £120
- PCB (control board) · from £220
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–£350, depending on the underlying cause.
Frequently asked questions
Can I fix a Protherm E7 fault myself?
Very little of the actual repair work is safe to carry out yourself. The one homeowner actions that are appropriate are: checking your gas supply is on, trying a reset (no more than two or three times), and checking for a frozen flue terminal. Everything else — cleaning or replacing electrodes, testing the gas valve, checking wiring, or replacing any internal component — must be done by a Gas Safe registered engineer. Working on gas appliances without the correct qualifications is both illegal and dangerous.
How much does it typically cost to fix a Protherm E7 error in the UK?
For the most common causes — electrode cleaning or replacement plus a call-out — most homeowners pay in the region of £120 to £200. If ignition leads or the spark generator also need attention, expect £150 to £280. A gas valve replacement typically adds up to around £200 to £350 including labour. In the minority of cases where a PCB is the root cause, the cost can climb to £400 or more, which is worth weighing against the age and overall condition of the boiler.
Why does the E7 code keep coming back after a reset?
A reset clears the lockout signal but does not fix the underlying fault. If E7 returns repeatedly, it means the root cause — dirty electrodes, a failing gas valve, a loose connection, or another issue — has not been addressed. Persistent re-lockouts are a strong signal to stop resetting and call a Gas Safe engineer, as repeated failed ignition attempts can stress components and occasionally indicate a gas supply problem that warrants prompt attention.
What is the difference between E7 and Eb on a Protherm boiler?
Both E7 and Eb point to an ignition system fault on Protherm boilers and are often used interchangeably across different model generations or firmware versions. If your display shows Eb, treat it the same as E7 — the causes and diagnostic process are identical. The variation is simply down to how different Protherm control boards render the same error on their displays.