Johnson & Starley E01 Fault Code: Causes, Fixes & Repair Costs
What does the Johnson & Starley E01 fault code mean?
The E01 code appears on Johnson & Starley boilers when the burner has failed to establish a flame after three consecutive ignition attempts. At that point the boiler shuts itself down — a condition known as ignition lockout — and holds the fault code on the display until the underlying problem is resolved and the unit is reset. The boiler is protecting itself and your home: running a burner that can't detect a proper flame would be unsafe. Common triggers range from something as simple as a temporary interruption to the gas supply, through to worn ignition or flame-sensing electrodes, a faulty gas valve, a blocked condensate siphon, or — in rarer intermittent cases — a failing PCB or, on Warmcair models, the ESYS ignition control module mounted on the gas valve.
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
- Interrupted or absent gas supply Common
If the gas cock at the boiler is closed, the meter has run out of credit, or there is a local network interruption, the burner simply has no fuel to ignite. This is the easiest thing to rule out first and costs nothing to check.
- Worn or mispositioned ignition or flame-sensing electrode Common
The ignition electrode produces the spark that lights the gas, while a separate detection electrode (sometimes the same probe on certain models) confirms a flame is present. If either electrode is cracked, heavily sooted, or the spark gap has drifted from the correct 4 mm setting, the boiler will either fail to light or light momentarily and then drop out, triggering E01.
- Insufficient gas pressure at the appliance Common
Even if gas is flowing, the inlet pressure must exceed 18 mbar for the burner to operate reliably. Low pressure — caused by a partially closed service valve, an undersized meter, or a fault on the network — prevents a stable flame from forming.
- Faulty or unpowered gas valve Sometimes
The gas valve controls fuel flow to the burner. If it is not receiving approximately 24 V DC from the PCB, or if the coil resistance between the outer pins measures other than around 114 Ω, the valve will not open correctly and ignition cannot succeed. Wiring harness damage between the valve and the PCB can produce the same result.
- Blocked condensate siphon or drain pipe Sometimes
A blockage in the condensate pipework or siphon assembly can cause the boiler to shut down and display a flame-failure code as the fault cascades through the control logic. In cold weather, a frozen external condensate pipe is a particularly common culprit.
- Fan fault or flue obstruction Sometimes
The PCB monitors fan speed before allowing ignition. If the fan is not reaching the correct speed — due to a failing motor, a seized bearing, or a blocked flue terminal — the control board will prevent ignition to avoid unsafe combustion conditions.
- Faulty ESYS ignition control module (Warmcair models) Sometimes
On Warmcair appliances the ESYS module sits directly on the gas valve and manages ignition sequencing. Failure of this module, or a loose connection on the flame-sensing electrode lead, can produce an intermittent E01 that resets and then reappears hours or days later — one of the more elusive presentations of this fault.
- Failing PCB or control board Rare
If all gas, electrode, and valve checks come back satisfactory but the boiler still enters ignition lockout — particularly if the fault is intermittent and the boiler runs perfectly when an engineer attends — the PCB itself may be misreporting or failing to process the flame-detection signal correctly. This is a relatively rare but known cause on older boards.
How to fix it
- Check that the gas supply is turned on and working DIY safe
Confirm the gas isolation valve at the boiler is fully open (handle in line with the pipe). Then check another gas appliance in the home — a gas hob, for example. If nothing gas-powered works, contact your gas supplier or check for a prepayment meter issue before going any further.
- Thaw a frozen condensate pipe if the weather is cold DIY safe
If the outside temperature is at or below freezing, locate the white plastic condensate pipe that exits the boiler and runs outside. Pour warm (not boiling) water along the pipe or wrap it in a warm cloth to thaw any ice blockage. Once clear, reset the boiler.
- Top up system pressure if it is below 1 bar DIY safe
Look at the pressure gauge on the boiler. If the needle is below 1 bar, use the filling loop (usually a braided hose with one or two valves beneath the boiler) to add water slowly until the gauge reads between 1 and 1.5 bar, then close the filling loop valves. Low pressure alone is unlikely to cause E01, but it is worth confirming everything is in order.
- Reset the boiler — up to two or three times only DIY safe
Press and hold the reset button (or follow the reset sequence in your user manual) to clear the lockout. Allow the boiler a full ignition cycle — usually 30 to 60 seconds — before deciding whether it has lit successfully. If it locks out again within a few attempts, stop resetting: repeated failed starts can mask a worsening problem and will not fix the underlying fault.
- Call a Gas Safe registered engineer to carry out a full ignition and gas-pressure diagnostic Gas Safe engineer
An engineer will measure gas inlet pressure (must exceed 18 mbar), inspect and test the ignition and flame-sensing electrodes (checking condition, position, and the 4 mm spark gap), verify that the gas valve is receiving the correct 24 V DC supply, and check the coil resistance of the valve (approximately 114 Ω between the outer pins). On Warmcair models, the ESYS module and its wiring connections will also be checked at this stage.
- Allow the engineer to inspect and clean or replace the electrodes and harness Gas Safe engineer
A cracked, sooted, or incorrectly positioned electrode is one of the most frequent causes of E01. The engineer will clean or replace the ignition and detection electrodes, check the high-tension lead for damage, and confirm all connections to the PCB are secure.
- Allow the engineer to check the fan, flue, and condensate assembly Gas Safe engineer
The engineer will verify that the fan runs at the correct speed before ignition is attempted, inspect the flue terminal for blockage or damage, and check the condensate siphon and drain for obstructions that could be causing the fault indirectly.
- Allow the engineer to replace any faulty components identified Gas Safe engineer
Depending on diagnosis, this may mean a new gas valve, ESYS module (Warmcair), fan motor, condensate siphon, or PCB. If the fault is intermittent and no single component is obviously to blame, the engineer may need a follow-up visit or may carry out a gas valve replacement as the most likely remaining cause before considering the PCB.
Parts you may need
- Ignition electrode and lead set · from £45
- Flame detection electrode · from £35
- Gas valve (manufacturer-matched) · from £120
- ESYS ignition control module (Warmcair) · from £85
- Flue fan / fan motor assembly · from £90
- Condensate siphon assembly · from £25
- PCB / main control board · from £160
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 fix Johnson & Starley E01 myself by just resetting the boiler?
A reset is a sensible first step and may clear a one-off nuisance lockout — for instance, if there was a brief blip in the gas supply. You can try resetting up to two or three times. However, if E01 returns each time, or keeps coming back over the following days, a reset is not a fix: it simply restarts the ignition sequence that the boiler has already failed three times. At that point you need a Gas Safe registered engineer to find and repair the actual cause.
Why does my Johnson & Starley boiler show E01 only sometimes, then work fine when the engineer arrives?
Intermittent E01 faults are one of the trickier presentations of this code. The most common culprits are a marginal flame-sensing electrode that works when cold but fails once it warms up, a loose connection on the detection electrode lead (particularly the ESYS module connection on Warmcair models), or a PCB that is beginning to fail. Engineers often need to carry out a live test during a fault episode or replace suspected components on a best-evidence basis. Keeping a note of when the fault appears — time of day, how long the boiler had been running, outdoor temperature — can help the engineer narrow it down faster.
How much does it cost to fix E01 on a Johnson & Starley boiler in the UK?
For the most common causes — electrodes, leads, or a gas valve — most homeowners pay somewhere between £120 and £380 including parts, labour, and any call-out fee. A straightforward electrode replacement at the lower end of that range is quite possible. A gas valve swap typically sits in the £200–£320 bracket once labour is included. If the PCB turns out to be the problem, the cost can rise above £400, and that is worth discussing with your engineer before authorising the work on an older boiler, as a replacement appliance may offer better value.
Is E01 dangerous? Should I leave the boiler alone until an engineer comes?
E01 means the boiler has locked out and is not running — it has already shut itself down as a safety measure. The immediate risk from an idle locked-out boiler is low. You should not smell gas; if you do, turn off your gas supply at the meter, open windows, and call the National Gas Emergency Service on 0800 111 999 immediately. Assuming there is no gas smell, the main concern is a loss of heating and hot water. Avoid repeatedly resetting the boiler, and do not attempt to interfere with the gas valve, electrodes, or any internal components yourself.