Ideal boiler L2 fault code: ignition lockout

What the boiler tried to do before it showed L2

On a heat demand the board runs the fan to purge the combustion chamber, then fires the spark at the electrode and opens the gas valve. A flame should establish within a couple of seconds, and the board then has to prove it exists. It does that by flame rectification: a small alternating voltage is applied to the sensing electrode, the flame conducts in one direction only, and the board reads back a tiny direct current in microamps through the burner and its earth path. No current means no flame as far as the board is concerned.

If it sees nothing it closes the gas valve, pauses and tries again, and when the last permitted attempt fails the display shows L2 with the reset symbol lit. That is why L2 is a useful code: the board got as far as calling for gas, so the demand, the fan and the ignition circuit all did something. The failure sits in the gas, in the flame, or in the sensing of it.

Every manufacturer logs that same event under its own label. A Vaillant F28 describes an ignition lockout in exactly the way L2 does, and a Vaillant F29 is the related code for a flame that lit and then went out. A Baxi E133 says the same thing a third way. The number changes with the badge on the case, the list of causes behind it barely moves, and the order those causes are worked through does not move at all.

One check narrows things before any of that. A boiler held off in lockout is not burning gas, so it takes the heating and the hot water together. If the radiators are warming normally and only the hot water has gone, you have no hot water but the heating works, the boiler is plainly firing, and an ignition lockout is not what you are dealing with.

Press reset twice, three times at the outside, no more. Every reset puts another charge of unburnt gas into the combustion chamber. Gas work is restricted by law to registered engineers, so nothing beyond the checks below should be attempted by anyone else. If you can smell gas, turn the gas off at the meter, open windows, leave the electrics alone and ring the national gas emergency line on 0800 111 999.

The two things to check yourself before calling an engineer

Two causes account for a large share of L2 calls and neither needs an engineer to spot. The first is that the boiler has no gas to light. Light a hob ring: if it burns a normal blue flame, gas is reaching the property, though that does not prove the supply at the boiler is sound. If nothing gas fired works, the problem is upstream at the meter, usually a prepayment meter out of credit, a smart meter in emergency credit or remotely shut off, or the emergency control valve left part turned after other work. If there is no hot water anywhere in the property and no code on the display at all, our no hot water checklist before you call covers that ground instead.

The second is condensate. Every Ideal condensing boiler drains acidic water through a plastic pipe, and where that pipe runs outside in small bore it freezes, backs water up into the trap and locks the boiler out. The timing gives it away: it fails first thing on a cold morning, it often runs a few minutes before stopping, and you may hear a gurgle before it cuts. Pour warm water, not boiling, along the exposed run, or lay a hot water bottle on it, then reset once the water moves. A pipe that freezes every winter wants rerouting.

• Light a gas hob ring to confirm gas is reaching the property
• Check a prepayment or smart meter for credit and for a remote disconnection
• Check the emergency control valve handle at the meter is in line with the pipe
• Follow the white plastic condensate pipe outside and feel for ice or a blockage
• Look at the flue terminal for a nest, leaves, render or snow across it
• Note what a reset actually does: silence, a fan run only, sparking with no ignition, or a light followed by a drop out

When the boiler lights and then locks out anyway

If you hear the spark, then a soft whoomph as the burner lights, and the boiler drops out three to five seconds later, a flame was established and the board did not see it. That is a rectification failure, which is electrode territory rather than gas supply territory.

Many Ideal boilers use a combined spark and sensing electrode, so one worn part does both jobs badly at once. The tip carbons up and insulates itself, the gap drifts open as the metal erodes, and a cracked ceramic lets the spark track to earth instead of jumping the gap. The lead and its boot degrade in the heat until the spark leaks before it arrives. All of it is cheap and consumable, and on a boiler years without a service it is the first place to look.

Earthing matters as much and gets missed. Flame current returns through the burner and the chassis, so a corroded burner fixing or a loose earth leaves you with a visible flame and a board reading nothing. An engineer measures that current in microamps with the burner alight and compares it against the manufacturer figure, which turns a guess into a reading. Lighting cleanly then dropping out as the boiler steps up to full rate is a different pattern, and points at gas pressure under load: low working pressure, a restricted supply, or a gas valve passing the wrong amount.

Condensate, flue and combustion faults that cause an L2

Inside the case, the condensate trap and siphon silt up with debris off an ageing heat exchanger. A part blocked trap lets the boiler run in mild weather and locks it out once the condensate rate rises in the cold. It strips, flushes and refills in minutes.

Flue faults give the same code. A terminal rendered over, sited too close to a boundary or positioned where the products recirculate starves the burner of clean air until the flame is unstable and the board loses it, and in a loft or riser a pushed apart flue joint does the same while being a safety matter in its own right. Fan speed is the last common mechanical cause: the board commands an ignition speed and reads it back, and a fan with worn bearings may still spin without holding that speed, giving an air to gas ratio the burner will not light on.

• Blocked condensate trap or siphon, or an external pipe with no fall
• Flue terminal blocked or recirculating, or a joint or seal parted on a hidden section
• Fan not holding commanded speed, so the air to gas ratio is wrong at ignition
• Worn, carboned or cracked ignition and sensing electrode, or a failed lead
• Poor earth continuity, so flame current cannot be read even with the burner alight
• Low gas working pressure, a restricted supply, or a gas valve out of adjustment

Why an Ideal boiler keeps showing L2 after a reset

A lockout that clears and then returns is still the same fault. The reset only clears the display, so the question worth answering is not how to reset it again but what pattern the returns follow, because an intermittent L2 is diagnosed from its behaviour as much as from anything measured on the day.

Three patterns cover most of them. A fault that appears on cold mornings and has cleared by the afternoon is a condensate pipe icing overnight. A fault that appears only when the hob or another gas appliance is also running is gas supply under load, which reads perfectly at rest and falls away the moment the burner asks for full rate. A fault that appears once the boiler has been running for a while, then goes away when it cools, is usually an electrode or a lead breaking down when hot, or an earth path that is marginal rather than open.

Write down the date, the time and the weather at every lockout. A boiler that has failed four times in a fortnight has already given you most of a diagnosis, and handing that over saves an engineer waiting for the fault to reappear.

What none of it justifies is resetting on a loop. Each reset puts another charge of unburnt gas into a chamber that has just failed to burn it, and an appliance reset repeatedly over weeks generally needs more work than it did when the code first appeared.

• Fails on cold mornings and clears by the afternoon: the condensate pipe is freezing
• Fails only when another gas appliance is running: working pressure is dropping under load
• Fails once the boiler is hot and runs again when cool: electrode, lead or earth breaking down with heat
• Fails at random with no pattern: flame sensing or the supply polarity and earth
• Keeps a written log of dates, times and weather for the engineer

What an engineer checks, and in what order

A proper L2 diagnosis runs in a sequence, and it is worth knowing so you can tell whether it is being done. Gas first, because it is quick and either clears half the possibilities or finds the fault outright. Then ignition and sensing. Then condensate, flue and combustion. The board is checked last, once everything it depends on has been proved good. That sequence is what the boiler diagnosis service is, and it is charged as time rather than as a part.

The same sequence is what tells you when to stop repairing. An appliance that has already had a gas valve or a board, is well past fifteen years old and is now locking out on L2 several times a week is no longer a repair question, and parts availability on older Ideal models is the practical limit rather than a matter of opinion. Our boiler replacement page sets out what that decision actually turns on, and an honest engineer will tell you which side of it you are on before you spend anything.

• Standing and working gas pressure at the inlet test point, with every appliance in the property running
• Flame current in microamps at the sensing electrode with the burner alight
• Electrode condition and gap measured against the manufacturer figures, and the lead tested
• Earth continuity from the burner back through the appliance
• Condensate trap stripped and flushed, and the external run checked for fall and freezing risk
• Flue integrity along its full length and the terminal position checked
• Combustion analysis at high and low rate before anything is signed off

Gas valves and control boards are the parts most often replaced on an L2 and the ones most often replaced without cause. Neither should be fitted on a hunch, and no gas valve should be adjusted without an analyser on the flue. If a part is being changed, ask which reading led to that.