This fault can involve incomplete combustion and carbon monoxide.
If anyone in the property feels sick, dizzy or drowsy, or you can smell gas: open the windows, leave the building, and do not switch anything on or off. Then call the National Gas Emergency Service.
0800 111 999Ideal L0d fault codewhat it means and how to fix it
A Logic Combi2 has locked out on ignition and blames the flue or condensate drain. Ideal's own first step is to check whether the condensate pipe is blocked or frozen.
Take care
What L0d means
L 0d is new with the three-character Logic Combi2, System2 and Heat2, and it is a more informative version of L2. Ideal's fault-finding menu routes it to the same section as the ignition lockout with the annotation "Blocked Flue/Condensate": the burner has failed to establish, and the board's combustion monitoring points at the exhaust side rather than the gas side as the reason.
On the text-screen Logic+ and Logic Max of the same year the fault appears as Blocked Flue/Condensate with three lines under it — check if the condensate pipe is blocked or frozen, check if the flue is blocked, if the fault persists contact the installer. That order is right. A condensing boiler makes water continuously and drains it through a small plastic pipe, and if that pipe freezes on an outside wall the water backs up into the boiler, the burner cannot hold a flame, and the boiler reports exactly this. Ideal's user guides carry a whole section on thawing it.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Frozen condensate pipe | The overwhelming cause in a cold snap, especially where the pipe runs outside in 22 mm rather than the 32 mm Ideal ask for. The boiler gurgles before it locks out. | Common |
| Condensate trap or pipe blocked with debris | The trap inside the boiler collects a grey sludge from the heat exchanger. Ideal's ignition chart includes checking the syphon and drain pipework for blockage. | Common |
| Flue terminal obstructed | A nest, a wasp trap, snow, or a new fence too close to the terminal. Ideal's second on-screen step is simply "check if flue blocked". | Occasional |
| Flue joint failed or flue disconnected | Rarer and more serious: exhaust recirculating into the air intake starves the burner and is a carbon monoxide risk. An engineer with a flue gas analyser finds this; a householder cannot. | Rare |
What to try yourself
Find the condensate pipe — the plastic pipe, usually white or grey, leaving the bottom of the boiler. Follow it to where it drains. If it runs outside and the weather is freezing, Ideal's advice is to thaw it with warm (not boiling) water or a hot water bottle along its length, working only on pipe you can reach from the ground.
Check the flue terminal outside for anything covering it — a nest, ice, a plastic bag. Look; do not poke anything into it.
Press Restart once. If the boiler lights and stays lit, the blockage was the cause. If L 0d returns, Ideal say contact the installer; do not keep resetting.
Get a Gas Safe registered engineer to look at your Ideal L0d
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What it costs to fix
Typical repair cost
£0–£300
Time on site
30 minutes
Nothing if you thaw it yourself. Insulating or re-running the condensate pipe £80–£200; clearing the trap and checking the flue at a service visit £70–£120; flue repairs from £150.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 28 September 2026
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Related Ideal fault codes
- F3Get it checkedThe fan is not running at the speed the boiler expects, so it cannot confirm the flue is clearing and has stopped the burner firing.Related: fan and flue
- L8Get it checkedThree meanings on three generations: a fan error on the Isar, Icos and Mexico HE; a PCB fault on the Logic ESP1; a reset button held over ten seconds on the Logic Combi2.Related: fan and flue
- F1Get it checkedSystem pressure has dropped below the minimum the boiler will run at. Topping it back up to 1.2 bar usually clears it straight away.Related: same brand
- L2Stop — call an engineerThe boiler failed to detect a flame during ignition and has locked out on the gas valve. Do not keep resetting it.Related: same brand
- F2Get it checkedThe flame was lost during operation. Ideal direct you to check the gas supply first, and that is genuinely the right order.Related: same brand
- L1Get it checkedThe boiler is not seeing enough water flow through it to run safely, so it has stopped. Usually a pump, an air lock, or a blocked filter.Related: same brand
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal L0d
Is L0d the same as L2?
It is a specific form of it. Both are ignition lockouts and Ideal send both to the same fault-finding section. L 0d carries the extra information that the board believes the flue or condensate route is the reason, which is why its on-screen steps are about pipes rather than the gas meter.
Which boilers show it?
Logic Combi2, System2 and Heat2 from 2023 as L 0d; Logic+ and Logic Max of the same year as Blocked Flue/Condensate in words. The ESP1 and earlier Logics report the same event as a plain L2, and their user guides tell you to check the condensate pipe as the first step of that code instead.
How do I stop the condensate pipe freezing again?
Ideal's guides list the options: insulate the external run, have it replaced with 32 mm pipe if it is smaller, shorten the external run, or have an installer fit a trace-heating kit or re-route it to an internal drain. In a cold spell, leaving the heating on low overnight keeps warm condensate moving through it.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.