Ideal L3 fault codewhat it means and how to fix it
The boiler has stopped because it cannot detect water moving through it. Ideal's own steps are to fill the system to 1 bar with it cold, bleed the radiators and try again.
Take care
What happened when you pressed Restart?
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.
It fired and the radiators warmed
Air was the cause. Watch the pressure over the next week; if it keeps needing topping up, the air is arriving because water is leaving somewhere.
L3 came straight back
The pump is not moving water even with the system full. It may be seized, unpowered or blocked, none of which a householder can reach.
Book an engineer; say the system is full and bled.
What L3 means
L3 is No Water Flow, and it is a lockout: the board has fired the burner, watched the temperature at the heat exchanger climb the way it only does when the water is standing still, and shut down before the exchanger cooks. It first appears as a code on the two-window Logic Code Combi ES and first-issue i-mini, and Ideal print the same fault in words — No Water Flow — on the text screens of the Logic+ and Logic Max from 2023 and as No Water Flow Fault on the Vogue.
The householder steps on the Logic+ screen are the useful part: with the boiler off and the system cold, fill to 1.0 bar; bleed the radiators; if the fault persists contact the installer. They are steps about water, not about the pump, because the most common reason a pump moves nothing is that there is air where the water should be.
The Vogue engineer chart takes over from there — is the system filled and every valve open, has the pump got its 230 volts and its wiring intact, and if all that is true, replace the pump.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Air in the boiler or system | A pump full of air spins without moving water. A system that has just been refilled, or has been losing pressure and topped up repeatedly, is the classic case, and it is why Ideal's steps start with filling and bleeding. | Common |
| Pump not running | Seized after a summer idle, or not receiving its supply. The Vogue chart checks the six-way connector and for 230 V at the pump before it condemns the pump itself. | Common |
| Valves closed | Isolation valves under the boiler, a failed zone valve or every radiator valve shut give the pump nowhere to send the water. Ideal ask for every valve to be open as the first question. | Occasional |
| Blocked heat exchanger or filter | Sludge is the slow version of the same fault. A system that has drifted from FU to L1 to L3 over a winter is telling you the circuit is silting up. | Occasional |
What to try yourself
Switch the boiler off and let it go cold. Ideal's instruction is specific about this: the filling and the reading are done with the system cold.
Bring the pressure up to 1.0 bar on the gauge using the filling loop, then bleed each radiator until water rather than air comes out, and top the pressure back to 1.0 bar afterwards.
Switch on and press Restart. If the radiators warm and the code stays away, the pump had lost its water. If L3 returns, Ideal say contact the installer — the pump or its supply is next, and that is engineer work.
Get a Gas Safe registered engineer to look at your Ideal L3
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–£350
Time on site
30 minutes
Nothing if filling and bleeding clears it. A pump fitted £180–£350 on a Logic.
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.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 28 September 2026
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
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
- 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: overheat and circulation
- FDGet it checkedNo water flow has been detected. The pump is the prime suspect and this will become an overheat if it is left.Related: overheat and circulation
- L AGet it checkedThe overheat thermostat on an Isar, Icos, Mexico HE or Esprit has tripped and the boiler has locked out. Ideal say hold reset for two seconds; if it recurs, switch off and call the installer.Related: overheat and circulation
- FUGet it checkedThe water leaving the boiler is more than 50°C hotter than the water coming back, which means very little of it is moving. Check the valves are open before anyone condemns the pump.Related: overheat and circulation
- F12Get it checkedThe pump rotor is jammed. Ideal's remedy is to clear the blockage — on a modern Logic that is an engineer freeing or replacing a sealed pump head, not a screwdriver in a bleed screw.Related: overheat and circulation
- F13Get it checkedThe board has lost proper communication with or control of the pump. Ideal group F13, F15 and F17 as one Pump Fault: check the pump wiring, and if that is sound replace the pump.Related: overheat and circulation
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal L3
Which Ideal boilers show L3?
As a code, the Logic Code Combi ES and the first i-mini, both with the two-window status and burner display; Ideal's FAQ lists it as "Flashing L AND 3 No Water Flow". Other Logic boards fold no-water-flow into L1, whose description reads "Flow Temperature Overheat or No Water Flow". Logic+, Logic Max and Vogue print No Water Flow or No Water Flow Fault on the screen. The Logic Max Heat and System have a dedicated flow sensor and show Fd.
Is running the pump dry going to have damaged anything?
A brief dry run is what the lockout exists to prevent turning into a long one. The boiler stopped itself before the heat exchanger reached a harmful temperature; the pump's bearings are water-lubricated and dislike running in air, but a few minutes will not have finished them.
Why does filling the system fix a pump fault?
Because most of the time it was never a pump fault. A centrifugal pump cannot move air, and a Logic that has been running at low pressure gathers air at the top of the heat exchanger and the pump housing. Refill, bleed, and the same pump moves water again.
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.