Ideal Icos HE and Icos System fault codes
Built 2004–2011
Same LED alternating display and code family as the Isar, with the differences a heat-only boiler brings: H 4 is the flue thermistor rather than the dry-fire thermistor, and there is no H 3 hot water thermistor.
Codes on the Icos HE and Icos System follow the same Ideal scheme as the rest of the range. Where a code behaves differently on this generation, the code page says so.
Ideal fault codes
Every published Ideal code. Open a code to see which models and years it applies to.
- F1System pressure has dropped below the minimum the boiler will run at. Topping it back up to 1.2 bar usually clears it straight away.Get it checked
- L2The boiler failed to detect a flame during ignition and has locked out on the gas valve. Do not keep resetting it.Stop — call an engineer
- F2The flame was lost during operation. Ideal direct you to check the gas supply first, and that is genuinely the right order.Get it checked
- L1The 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.Get it checked
- F3The fan is not running at the speed the boiler expects, so it cannot confirm the flue is clearing and has stopped the burner firing.Get it checked
- FDNo water flow has been detected. The pump is the prime suspect and this will become an overheat if it is left.Get it checked
- F4The 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.Get it checked
- F5The 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.Get it checked
- L5Two 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.Get it checked
- F9The control board has not been told what boiler it is in, or has failed. L9 is the same fault locked out. The 2011 Logic Combi row also covers a gas valve short circuit.Get it checked
- LCYou have reset the appliance five times in fifteen minutes. This is not a fault in itself — it is the boiler asking you to stop.Usually simple to fix
- L FAn Isar, Icos, Mexico HE or Esprit has made three attempts to light and locked out; the LED window flashes L then F. Ideal permit one reset and a gas supply check, then an engineer.Stop — call an engineer
- dUNot a fault. The diverter valve has been parked in its mid-position for servicing and the boiler is waiting to be told the service is over. Ideal publish the way out.Usually simple to fix
- Blank displayNothing on the screen at all. Ideal's user guides send you to the boiler's switch and the consumer unit first; the installer charts then work from the terminal block to the board.Get it checked
- L3The 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.Get it checked
- L6A flame is being detected when there should not be one. Turn the appliance off and call a Gas Safe engineer rather than resetting it.Stop — call an engineer
- F7The mains voltage reaching the boiler has dropped below what the board will run on. Ideal's advice is an electrician or your electricity supplier, not a heating engineer.Get it checked
- L AThe 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.Get it checked
- FUThe 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.Get it checked
- H AA temporary code with two meanings. On an Isar it is low water pressure and Ideal say fill to 1 bar; on a gaugeless Mexico HE, Ideal send you to the radiator valves.Get it checked
- L0dA Logic Combi2 has locked out on ignition and blames the flue or condensate drain. Ideal's own first step is to check whether the condensate pipe is blocked or frozen.Get it checked
- C0The board cannot activate the Boiler Chip Card that tells it what model it is fitted to. Ideal's engineer check is whether the small plastic card is in its slot at all.Get it checked
- L9On a Logic, L9 is the locked-out form of the unconfigured-board fault F9. On an Isar HE it is something else entirely: a heat exchanger overheat read by the dry-fire thermistor.Get it checked
- F6The 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.Get it checked
- SEA service reminder, not a fault. The installer set a timer at the last visit and it has run down. Ideal's advice is to contact the installer, who resets it when the boiler is serviced.Usually simple to fix
- C2The Boiler Chip Card in the control board is wrong for this boiler, missing from an unprogrammed board, or has failed. Ideal's sequence ends with a new card, then a new PCB.Get it checked
- F12The 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.Get it checked
- FAThe 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.Get it checked
- L8Three meanings on three generations: a fan error on the Isar, Icos and Mexico HE; a PCB fault on the Logic ESP1; a reset button held over ten seconds on the Logic Combi2.Get it checked
- F0On 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.Get it checked
- F13The 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.Get it checked
- F16The board has detected a fault in the gas valve or its wiring. Nothing here is for a householder to try; Ideal's checks cover the valve's supply and coil and end with replacing it.Stop — call an engineer
- F0tA Logic Combi2 has lost contact with its room thermostat. Ideal's user guide says to check the thermostat's batteries; the installer manual adds its connections.Get it checked
- F0CThe 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.Get it checked
- Thermal Fuse LockoutA Vogue has stopped because the one-shot thermal fuse on its heat exchanger reads open circuit. Ideal allow one reset; if the message returns, the fuse has usually blown and the heat exchanger is replaced.Get it checked
- F10The spark generator on a Logic Combi2 — the unit that makes the ignition spark — has failed a self-check. Ideal's instruction is to check its wiring and, if that is sound, replace it.Get it checked
- L EA board error on an Isar, Icos, Mexico HE or Esprit. L E is the locked-out form and H E the temporary one; Ideal try a reset and a power cycle, then replace the PCB.Get it checked
- F14The mains voltage reaching a Logic Combi2 is too high for the board to run on. It is the mirror image of F7, and Ideal's instruction is the same: contact your electricity provider.Get it checked
- H 1The control thermistor on the flow pipe of an Isar, Icos, Mexico HE or Esprit is reading wrongly. Ideal test its resistance and the wiring to the board, then replace the sensor or the PCB.Get it checked
- Pump Dry RunA Logic+ or Logic Max text screen saying the pump is turning with no water to move. Ideal's steps are the filling ones: boiler off and cold, fill to 1.0 bar, bleed the radiators, refill.Get it checked
- H 3The hot water thermistor on an Isar HE combi is reading outside its range. Heating usually carries on; the taps suffer. Ideal test the sensor on the plate heat exchanger, then wiring, then board.Get it checked
- H 4On an Isar HE, H 4 is the dry-fire thermistor on the heat exchanger; on an Icos HE it is the flue thermistor. Both guard against running hot with no water.Get it checked
- H FThe flame detection electrode on an Isar, Icos, Mexico HE or Esprit has failed Ideal's continuity test — a short circuit, in the Icos wording. The electrode is replaced, or the board.Get it checked
- No Connection To Primary PCBThe Vogue's screen has lost contact with the control board behind it. Ideal's first move is to turn the power off and on; if it returns, the lead between the boards is an engineer's job.Get it checked
- uPA new or reset control board waiting to be programmed. Ideal's manual shows uP as the first thing a replacement PCB displays, before F9, until the installer tells it what boiler it is in.Get it checked
- Flow/Return Thermistor FaultA Vogue Gen2 or Vogue Max message naming both temperature sensors at once. Ideal's checks are whether each thermistor is clipped securely to its pipe and whether both read the right resistance.Get it checked
- H 2The return thermistor on an Isar HE is reading outside its range. It is the temporary partner of H 1 and Ideal test it the same way; it is not listed on the heat-only Icos.Get it checked
- H nAn Isar, Icos, Mexico HE or Esprit has detected that its live and neutral are the wrong way round. Ideal's entire remedy is to check the wiring to the boiler — an electrician's job.Get it checked
- PCB ReplacedNot a fault. A Vogue shows PCB Replaced once a new primary board has been fitted and programmed, and Ideal's whole instruction for it is to restart the boiler by pressing RESTART.Usually simple to fix
- PCB Replaced IncorrectlyA first-generation Vogue message: the new primary board has the wrong Boiler Chip Card, or none. Ideal's two checks are that the card is fitted correctly and that it is the right one.Get it checked