Ideal Boiler Fault Codes: F1, F2, L2 and What to Do

Ideal boiler fault codes come in two groups. F codes are faults the boiler has detected: F1 is low water pressure, F2 is flame loss, F3 is a fan fault, F4 and F5 are the flow and return temperature sensors, and F6 is the outside sensor. L codes are lockouts, where the boiler has shut down for safety: L1 is overheat or no water flow, L2 is ignition lockout and L6 is false flame lockout. LC means it has been reset five times in 15 minutes. Most homeowners see F1, L1 or L2, and those are the ones you can often clear yourself by checking the pressure, the gas supply and the condensate pipe. If a code comes back after one restart, it needs a Gas Safe engineer.

F codes and L codes

An F code usually means the boiler has spotted a problem and is waiting. Fix the cause, such as low pressure, and it often starts again by itself or after a restart. An L code means the boiler has locked out. It tried to do something, such as light the burner, failed in a way that could be unsafe, and shut down. It won't run until you press restart.

Before you look anything up, note the model name on the front of the boiler (Logic, Logic+, Vogue, Instinct, Exclusive and so on) and write the code down exactly. Ideal uses much the same codes across its ranges, but a few differ between older and newer models, so the fault table in your own user guide has the final word.

Ideal fault codes at a glance

Code	What Ideal says it means	What you can check
F1	Low water pressure	Gauge should read 1 to 1.5 bar. Top up with the filling loop.
F2	Flame loss	Other gas appliances, gas meter, prepayment credit.
F3	Fan fault	Restart once. If it returns, call an engineer.
F4	Flow thermistor (temperature sensor)	Restart once, then engineer.
F5	Return thermistor	Restart once, then engineer.
F6	Outside sensor fault	Only on boilers with a weather sensor fitted. Restart, then engineer.
F7	Low mains voltage	An electrical supply problem, not a boiler part. Ideal's guide says to contact an electrician or your electricity supplier.
L1	Flow temperature overheat or no water flow	Pressure at 1 to 1.5 bar, radiator valves open.
L2	Ignition lockout	Condensate pipe, other gas appliances, meter and credit.
L6	False flame lockout	Restart once, then engineer.
LC	Five resets within 15 minutes	Turn the power to the boiler off and on. Stop resetting.
d	Diverter valve set to mid-position for servicing (Logic Code Combi)	Turn the knobs fully clockwise, switch the power off and on, press restart.

Sources: Ideal's fault code FAQ and the fault code table in the Logic Code Combi ESP1 user guide. On some models L5 appears alongside a return sensor fault, while Ideal's general list uses L5 for too many resets, which is why checking your own manual matters.

F1 and L1: pressure and water flow

F1 means the water pressure in the heating system has dropped too low for the boiler to run safely. Look at the gauge on the front or underneath the boiler. Ideal's guide says it should read between 1 and 1.5 bar with the heating cold. If it's lower, top it up using the filling loop, the braided hose or key under the boiler, following your user guide. Our guide on how to repressurise a boiler walks through it step by step.

Topping up is the easy part. If you have to do it again within days or weeks, water is escaping somewhere: a weeping radiator valve, a pressure relief valve discharging outside, a failed expansion vessel or a leak under the floor. See why a boiler keeps losing pressure for how to narrow that down, and our full Ideal F1 guide.

L1 means the water leaving the boiler got too hot, usually because not enough water was moving through it. Ideal's first check is the same: pressure between 1 and 1.5 bar. Also make sure the radiator valves haven't all been turned off, because a boiler with nowhere to send its heat will overheat. If the pressure is right and L1 keeps coming back, the usual causes are a failing pump, sludge, a blocked filter or a sensor, which is engineer territory. More in our Ideal L1 guide.

F2 and L2: flame loss and ignition

Both codes are about the burner. F2 means the boiler lit, then lost the flame. L2 means it tried to light, didn't detect a flame and locked out. The checks you can make are the same for both:

1. Check that other gas appliances, such as the hob, are working. If none are, the problem is the gas supply rather than the boiler.
2. Check the gas meter is on and, if you have a prepayment meter, that it has credit. A recent top-up after running out can leave air in the supply.
3. For L2 in cold weather, check the condensate pipe. Ideal's user guide says a blocked condensate pipe makes a gurgling noise before the boiler locks out on L2. It's the white or grey plastic pipe running outside to a drain. Pour warm, not boiling, water over the frozen section at ground level only.
4. Restart the boiler once.

If other gas appliances work, the condensate pipe is clear and the code returns, the cause is usually inside the boiler: the ignition electrode, flame sensing, the gas valve or the PCB. That work needs a Gas Safe engineer. Our Ideal L2 guide and Ideal F2 guide go into more detail, and our condensate pipe page covers a pipe that keeps freezing.

If you smell gas at any point, stop. Don't restart the boiler or use switches. Open windows, turn off the gas at the meter if you can, leave the property and call the National Gas Emergency Service on 0800 111 999. See our guide on what to do if you smell gas.

F3 to F6 and L6: parts faults

These codes point at a specific component rather than something you can adjust from outside the boiler:

• F3, fan fault. The fan pushes air through the burner and out of the flue. If the boiler can't confirm the fan is running at the right speed, it won't light. A fan that has started to whine or rattle can be an early sign.
• F4 and F5, flow and return thermistors. These sensors tell the boiler the water temperature. A faulty sensor or loose connection gives a reading the boiler can't trust.
• F6, outside sensor. Only relevant if a weather compensation sensor has been fitted on an outside wall. A damaged cable or sensor triggers it.
• L6, false flame lockout. The boiler detected a flame when there shouldn't be one. It's a safety lockout and needs checking.

For all of these, Ideal's advice is to restart the appliance once and, if it fails to operate, contact Ideal while the boiler is under warranty or a Gas Safe registered engineer if it isn't. Don't open the casing. HSE's guidance explains how to check an engineer is registered for the work.

Restarting, and what LC means

On most Ideal boilers you restart by pressing the restart button. On some models you turn the control knob to the reset position for a few seconds. Our guide on how to reset a boiler covers the general method.

Restart once, after you've dealt with the likely cause. Pressing restart again and again doesn't fix anything, and Ideal boilers count it: five resets within 15 minutes shows LC. Ideal's guide says to turn the electrical supply to the boiler off and on at that point, and to call an engineer if it still won't work.

When to call an engineer

Call a Gas Safe engineer when:

• F1 comes back within a few days of topping up, or the pressure won't hold.
• L1 returns with the pressure correct and radiators open.
• F2 or L2 returns when other gas appliances work and the condensate pipe is clear.
• You see F3, F4, F5, F6 or L6 after one restart.
• LC appears and switching the power off and on hasn't helped.

If the boiler is still under Ideal's warranty, contact Ideal first, as the warranty terms may require it. Outside warranty, our engineers repair Ideal boilers across London. See our boiler repair and boiler lockout services.

We charge £95 an hour for labour, plus a £60 call-out that's waived when the job runs over 2 hours. Parts are extra, and we confirm the price before any work starts. The pricing page explains how jobs are charged. For codes from other makes, see our Worcester, Baxi and Vokera code guides.

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