Ideal L5 fault codewhat it means and how to fix it
Two different faults share this code. On the two-window Logic ES boards it means five resets in fifteen minutes; on the 2011 Logic, the ESP1 and the Combi2 it is a return thermistor lockout.
Take care
What does the display look like?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Two small windows marked status and burner
L5 is five resets in fifteen minutes. Power off and on at the fused spur clears the counter; the fault you were resetting has not gone anywhere.
Power cycle once, then find the original code.
One window showing L5 or L 05
This is the return thermistor lockout that pairs with F5. Restart once; if it returns the sensor needs an engineer.
Read the F5 page and book an engineer if it repeats.
What L5 means
Look at the display before you read on. If your Ideal has two small windows side by side, labelled status and burner, with the letter in one and the number in the other, you have a 2012–2015 Logic ES, Logic Code Combi ES, Independent C, ProCombi or first-issue i-mini, and Ideal's table for that board gives L5 as "5 Boiler Resets in 15 minutes". It is not a component fault. The board has counted five presses of the reset button in a quarter of an hour and has decided that whatever is wrong is not going to be solved by a sixth.
If instead the letter and number sit together in one window — the 2011 Logic, or the ESP1 showing L 05, or the Combi2 — L5 is the return thermistor lockout that pairs with F5, and the return thermistor page is the one to read. The two meanings share nothing but the digit, and Ideal's own guides for the two boards disagree with each other in print.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Repeated resets chasing an underlying lockout | On the ES boards the code is caused by the person at the boiler, not by a part. Something else — usually an ignition or overheat lockout — kept returning and was reset five times. | Common |
| Return thermistor open, shorted or off its pipe | On the single-window Logic, ESP1 and Combi2 boards this is the return sensor having failed the same resistance test as F5, and it wants the same fix. | Common |
| A sticking or shorted reset button | Rare, but an ES board that shows L5 when nobody has touched it is registering presses it did not receive from a finger. | Rare |
What to try yourself
Identify the display. Two labelled windows means the reset-counter meaning applies; one window means the thermistor meaning applies and you should stop here and read the F5 page instead.
For the reset-counter meaning, Ideal's action is to turn the power off and on at the fused spur — the switch near the boiler with the 3 amp fuse in it — not to press the button again. Wait a minute with it off.
When it powers back up, watch for the code that was being reset before L5 appeared. That code is the actual fault, and it is the one to report if the boiler does not run.
Get a Gas Safe registered engineer to look at your Ideal L5
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–£160
Time on site
10 minutes
Nothing for the reset counter itself. For the thermistor meaning, £80–£160 fitted, as for F5.
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.
Ideal Logic flow or return thermistor (clip-on NTC)
£12–£35Authorised Ideal parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Ideal fault codes
- F4Get it checkedThe flow thermistor — the sensor reading the temperature of water leaving the heat exchanger — is giving a value the board will not accept. L4 is the same fault as a lockout.Related: sensors and thermistors
- F5Get it checkedThe return thermistor on the pipe bringing water back from the radiators is reading outside its range. On most Logic boards L5 is the locked-out form of the same fault.Related: sensors and thermistors
- F6Get it checkedThe outside sensor for weather compensation is reading wrongly or is not connected. It only appears on boilers that have one, or have been told they have one.Related: sensors and thermistors
- FAGet it checkedThe return pipe is reading hotter than the flow, which cannot happen in a boiler that is plumbed and sensing correctly. Ideal call it a negative differential; the Vogue screen says Flow/Return Reversed.Related: sensors and thermistors
- F0Get it checkedOn the Logic Code Combi ES and first i-mini, F0 is the sensor that detects water flow reporting a fault. It is not the same as L3, which is the flow itself having stopped.Related: sensors and thermistors
- F0CGet it checkedThe hot water thermistor on a Logic Combi2 or i-mini2 is out of range. Heating usually carries on; the tap side suffers, because the board can no longer see the water it is making.Related: sensors and thermistors
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal L5
Why did Ideal give one code two meanings?
The two-window ES boards introduced in 2012 had no LC in their table; five-resets moved to L5, and the return thermistor was printed as F5 only. The ESP1 that followed in 2015 went back to LC for resets and restored L5 as the thermistor lockout. Both tables are Ideal's own, and both are still on boilers in service.
How do I tell an ES board from an ESP1 without the manual?
Count the windows. The ES generation shows the letter and the number in two separate little panels with the words status and burner printed above them. The ESP1 has one display showing two characters together, F 01 or L 05, alternating with the flow temperature.
Does the reset counter mean something is wrong?
It means something was wrong five times in fifteen minutes. The counter itself is harmless and clears when the power is cycled, but it exists because repeatedly commanding a boiler to light into a fault is not a repair. Whatever lockout you were clearing is the thing that needs attention.
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
- Manufacturer support portal
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.