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Ideal boiler error codes

18 codes that Ideal Heating publishes for its boilers, each with what it means, the likely cause, what you can safely check and when to call a Gas Safe registered engineer. Tap your code:

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone. Anything else is for a Gas Safe registered engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999. Codes that need one are marked Gas Safe engineer.

Read this first

Ideal Logic boilers show an F code (a fault) or an L code (a lockout) on the display, written with a zero: F01, L02. Ideal’s own fault-code FAQ writes the same codes without it (“L2”, “F1”), and the lookup finds either. This page follows the fault-code table of the Logic Combi2 user guide (10.2023), all 18 of its fault codes. For almost every one, Ideal gives the householder a first step — check the pressure, check the gas, clear the condensate pipe, or press restart — and then says: if the boiler still fails to operate, contact Ideal while it is under warranty, or a Gas Safe Registered Engineer after that. The table also lists Ud, which is not a fault: the diverter valve set to its mid-position for a service.

F01 Low water pressure

What it means
The heating system water pressure is too low.
Likely cause
Water lost from the heating system.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Check the system pressure gauge reads between 1 and 1.5 bar.
  • If it is low, re-pressurise the system as the guide’s section 3 shows.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

L01 Overheat or no water flow

What it means
The flow temperature overheated or no water is flowing.
Likely cause
Low pressure or no circulation in the heating system.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Check the system pressure gauge reads between 1 and 1.5 bar.
  • If it is low, re-pressurise the system as the guide’s section 3 shows.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F02 Flame loss

What it means
The flame was lost.
Likely cause
No gas reaching the boiler, among other causes.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Check that your other gas appliances work, to confirm there is gas in the property.
  • If they do not, or there are none, check the gas is on at the meter and that a prepayment meter has credit.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

L02 Ignition lockout

What it means
The boiler failed to light and locked out. It also locks out with L02 when the condensate pipe is blocked — often frozen in cold weather.
Likely cause
A blocked or frozen condensate pipe, or no gas reaching the boiler.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Check the condensate pipe for blockages. A blocked or frozen pipe makes a gurgling noise before the boiler locks out; thaw a frozen one at ground level only, with a hot water bottle, heat pack, warm damp cloth or warm (never boiling) water, then restart.
  • Check that your other gas appliances work, to confirm there is gas in the property.
  • If they do not, or there are none, check the gas is on at the meter and that a prepayment meter has credit.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

L0d Blocked flue or condensate

What it means
The flue or the condensate drain is blocked.
Likely cause
A blocked condensate pipe (often frozen) or flue.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Check the condensate pipe for blockages. A blocked or frozen pipe makes a gurgling noise before the boiler locks out; thaw a frozen one at ground level only, with a hot water bottle, heat pack, warm damp cloth or warm (never boiling) water, then restart.
  • Check that your other gas appliances work, to confirm there is gas in the property.
  • If they do not, or there are none, check the gas is on at the meter and that a prepayment meter has credit.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F03 Fan fault

What it means
A fault with the fan.
Likely cause
Not stated beyond “fan fault”.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Press the restart button once. The boiler repeats its ignition sequence.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F04 L04 Flow thermistor

What it means
A fault with the flow thermistor, the sensor on the water going out to the radiators.
Likely cause
A sensor fault.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Press the restart button once. The boiler repeats its ignition sequence.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F05 L05 Return thermistor

What it means
A fault with the return thermistor, the sensor on the water coming back.
Likely cause
A sensor fault.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Press the restart button once. The boiler repeats its ignition sequence.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F06 Outside sensor failure

What it means
The outside (weather compensation) sensor has failed.
Likely cause
A sensor fault.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Press the restart button once. The boiler repeats its ignition sequence.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

L06 False flame lockout

What it means
The boiler saw a flame when it should not have, and locked out.
Likely cause
A flame-sensing fault.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Press the restart button once. The boiler repeats its ignition sequence.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

L0C Five resets in 15 minutes

What it means
The boiler has been reset five times within 15 minutes.
Likely cause
Repeated resets of a fault that keeps coming back.
What you can safely check

Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.

  • Turn the electrical supply to the boiler off and on.
When to call a Gas Safe registered engineer
If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F07 Low mains voltage

What it means
The mains electricity voltage reaching the boiler is too low.
Likely cause
The electricity supply to the property or the boiler.
What you can safely check

Nothing for the owner to check: this one is for a Gas Safe registered engineer.

When to call a Gas Safe registered engineer
Gas Safe engineer Contact a qualified electrician or your electricity provider, as Ideal’s guide says.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F09 L09 Unconfigured circuit board

What it means
The circuit board is unconfigured or faulty, or the gas valve has short-circuited.
Likely cause
A circuit board or gas valve fault.
What you can safely check

Nothing for the owner to check: this one is for a Gas Safe registered engineer.

When to call a Gas Safe registered engineer
Gas Safe engineer If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F0U Flow and return more than 50°C apart

What it means
The water going out is more than 50°C hotter than the water coming back.
Likely cause
Not stated beyond the temperature difference.
What you can safely check

Nothing for the owner to check: this one is for a Gas Safe registered engineer.

When to call a Gas Safe registered engineer
Gas Safe engineer If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

F0C Hot water thermistor fault

What it means
A fault with the domestic hot water thermistor.
Likely cause
A sensor fault.
What you can safely check

Nothing for the owner to check: this one is for a Gas Safe registered engineer.

When to call a Gas Safe registered engineer
Gas Safe engineer If the boiler fails to operate, contact Ideal while it is under warranty, or a Gas Safe registered engineer after the warranty period.

Source: Ideal Heating, Logic Combi2 user guide (10.2023, UIN 237664 A01): 1.9 fault codes Checked 2026-09-28.

A code that is not listed here

Other Ideal ranges (Logic Max, Vogue, Exclusive, older Logic models) have their own guides on idealheating.com, and a code may differ between them. For a code not here, Ideal’s guide says to consult a Gas Safe Registered Engineer.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Related pages

Source

Every code on this page comes from these pages, published by Ideal Heating and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.