The L6 code means your boiler has detected a flame when there shouldn’t be one — specifically when no heating or hot water demand is active and the gas valve should be fully closed. In plain terms, the boiler thinks it’s seeing a flame where none should exist, and has locked out as a safety precaution.
That’s the right response. A boiler that’s detecting flame signals it can’t explain should not be running.
An L6 fault on your Ideal boiler is one of the more serious codes you can see on the display — and it’s one of the Ideal fault codes that needs to be taken seriously rather than dismissed with a few resets.
At The Edinburgh Boiler Company, our Gas Safe registered engineers work across Edinburgh, the Lothians and central Scotland, and when we see an L6 on an Ideal boiler, we treat it as a priority call. Here’s why.
What exactly is a “false flame lockout”?
Your Ideal boiler has a flame detection electrode inside the combustion chamber. Its job is to confirm a flame is present when the boiler is firing, and to confirm there is no flame when the gas valve is closed. The PCB checks this constantly.
When the boiler is off — sitting in standby, waiting for a demand — that electrode should be reporting nothing. If it reports a flame signal when the gas valve is shut, the PCB registers that as a false flame, locks the boiler out, and displays L6. It’s essentially the boiler saying: “Something doesn’t add up here, and I’m not going to keep running until someone figures out what.”
What causes the Ideal L6 fault?
There are three main causes, and all of them require a Gas Safe registered engineer to diagnose and fix safely:
- Faulty flame detection electrode — the most common cause. The electrode may have deteriorated, cracked, or developed a fault that causes it to send a false signal to the PCB even when there’s no flame. It may need cleaning, repositioning, or replacing entirely.
- Sticking or leaking gas valve — a gas valve that isn’t closing fully will allow a small amount of gas to leak into the burner, which can produce a residual flame or flame signal even when the boiler isn’t firing. This is a gas safety issue and should never be investigated by anyone other than a Gas Safe engineer. If the valve is completely broken, it may not respond to the PCB at all.
- Faulty PCB — the control board processes all signals from the flame electrode. If the PCB is misreading or generating false signals internally, it can trigger an L6 lockout even when the electrode and gas valve are functioning correctly. PCB faults tend to come with other erratic boiler behaviour, so if your boiler has been acting strangely in other ways before the L6 appeared, that’s worth mentioning to the engineer.
What can you do yourself?
Very little, and that’s not us being overly cautious — it’s genuinely the nature of this fault. Because L6 involves potential gas valve issues and flame detection, it falls firmly outside the scope of homeowner troubleshooting.
The two things you can reasonably try before calling an engineer are:
- Reset the boiler — press and hold the reset button for a few seconds, or turn the dial to the reset position as described in your Ideal manual. If the boiler fires up and runs normally, keep a close eye on it.
- Power cycle the boiler — switch the electrical supply off at the fuse spur, wait 30 seconds, and turn it back on. This clears any temporary electronic glitch that might have triggered a false reading.
If the L6 code comes back after either of those steps, don’t keep resetting. Switch the boiler off and call a Gas Safe registered engineer.
It’s also worth quickly checking that other gas appliances in the property — the hob, oven or gas fire — are working normally. If none of your gas appliances are working, the issue may be with your gas supply rather than the boiler itself, in which case contact your gas supplier or National Gas on 0800 111 999.
Why you shouldn’t keep resetting an L6 fault
With some fault codes, a reset is a perfectly sensible first response. With L6 it’s different. If the boiler is detecting flame signals when the gas valve should be closed, there’s a possibility — however small — that gas is reaching the burner when it shouldn’t be. Repeatedly resetting the boiler in that situation isn’t just ineffective, it could be unsafe.
One reset, one power cycle — that’s reasonable. After that, the boiler should stay off until an engineer has established what’s causing the false flame signal.
When to call The Edinburgh Boiler Company
If the L6 fault persists after a reset, or keeps coming back, it’s time to get a Gas Safe registered engineer out promptly. Our engineers at The Edinburgh Boiler Company are experienced with Ideal Logic, Vogue and other Ideal combi and system boilers across Edinburgh and the Lothians, and an L6 fault is always treated as a priority.
Depending on what we find, we can:
- Test and replace the flame detection electrode
- Inspect and, where necessary, replace a faulty or sticking gas valve
- Diagnose PCB faults and advise on repair or replacement
- Carry out a full safety inspection of the combustion components while we’re there
Because L6 involves components directly linked to gas combustion, it’s not a fault where we’d recommend waiting to see if it resolves itself.
Can a boiler service prevent the L6 fault?
In some cases, yes. Flame electrode deterioration and early signs of gas valve wear are things a thorough annual boiler service can pick up before they develop into a full lockout.
Our Gas Safe engineers carry out annual boiler servicing across Edinburgh and the Lothians, and as part of that service we inspect combustion components, check electrode condition, and test the gas valve operation.
It won’t catch every possible cause of an L6 fault, but it significantly reduces the chances of being caught out by one.
Is it worth repairing or time for a new boiler?
A flame electrode replacement is a relatively minor repair. A gas valve replacement is more involved but still a standard job for an experienced engineer. PCB replacement sits at the higher end of repair costs, and on an older boiler it’s worth having an honest conversation about whether it makes financial sense compared to putting that money towards a new installation.
As accredited Ideal and Worcester Bosch installers, we replace boilers across Edinburgh every day. A new A-rated combi boiler comes with up to a 12-year manufacturer warranty when fitted by an accredited installer, and we can typically have one installed within 48 hours of your first call.
We’ll always give you a straight answer on whether repair or replacement is the right move — and we’ll never push you towards a new boiler if a repair is the sensible option.
Ideal L6 fault — key facts
- L6 = false flame lockout — the boiler has detected a flame signal when the gas valve should be fully closed
- Not a DIY fix — this fault involves gas combustion components and must be diagnosed by a Gas Safe registered engineer
- Most common causes: faulty flame detection electrode, sticking or leaking gas valve, PCB fault
- Quick homeowner steps: one reset, one power cycle, check other gas appliances are working — then call an engineer if L6 persists
- Don’t keep resetting — repeated resets on a potential gas valve fault are not safe
- Best prevention: annual boiler service to check electrode condition and gas valve operation
The Edinburgh Boiler Company are Gas Safe registered specialists in boiler installation, repair and annual servicing across Edinburgh, the Lothians and central Scotland. Contact us for a same-week repair visit, or a free quote on a new Ideal or Worcester Bosch boiler.
FAQs
Is the Ideal L6 fault dangerous?
It can be, which is why the boiler locks out immediately. The L6 code means the boiler is detecting a flame signal when the gas valve should be shut — in the worst case, that could indicate gas is reaching the burner when it shouldn’t be. Don’t keep resetting and treat it as a priority call to a Gas Safe engineer.
Could the Ideal L6 fault be caused by a recent boiler service?
Potentially, yes. If the flame electrode was disturbed, repositioned incorrectly, or a connection was not fully secured during a service, it could cause a false flame signal. If your L6 fault appeared shortly after a service visit, mention that when you call — it helps the engineer pinpoint the cause faster.
How long does it take to fix an Ideal L6 fault?
It depends on the cause. An electrode replacement is usually a quick job completed in a single visit. A gas valve replacement takes longer and involves gas work, so your engineer will need to isolate the gas supply during the repair. A PCB replacement can vary depending on parts availability. At The Edinburgh Boiler Company, we’ll give you a clear diagnosis and fixed quote before any work begins.
