UK
Ideal error codes
Ideal boilers show a fault as a letter and a number flashing on the display, such as F and 1 or L and 2. Ideal uses different codes on different models for some faults: F4 and L4 are both the flow thermistor, for example, and F2 and L2 are both flame loss or ignition lockout. Most of Ideal's advice starts with a reset, then an engineer if the code comes back.
- 13 codes
- Boilers
- Checked against official pages
Boilers 13 codes
F1 Water pressure too low
The water pressure in the heating system is too low.
F2 Flame loss (went out or won't light)
The boiler lost its flame or couldn't light, so it has stopped.
L2 Ignition lockout (boiler won't light)
The boiler tried to light and couldn't, so it has locked out.
L1 Overheated or no water flow
Ideal lists L1 as flow temperature overheat or no water flow.
FD No water flow
Water isn't flowing through the boiler as it should, so it has stopped.
F3 Fan fault
There's a problem with the boiler's fan.
F4 Flow thermistor fault
There's a fault with the flow thermistor, a temperature sensor inside the boiler.
L6 False flame lockout
Ideal lists L6 as a false flame lockout: the boiler has sensed a flame when it shouldn't have, and has locked out.
F5 Return thermistor fault
There's a fault with the return thermistor, the temperature sensor on the water coming back from the radiators.
F6 Outside sensor fault
The boiler isn't getting a proper reading from its outside (weather) sensor, the sensor that tells it the temperature outdoors.
F7 Mains voltage too low
The boiler isn't getting enough voltage from your electricity supply.
LC Reset too many times
The boiler has been reset five times within 15 minutes, so it's blocking further resets.
FU Flow and return temperatures too far apart
The water coming back from the radiators is far colder than the water leaving the boiler, more than 50 degrees apart.
No codes of that type for this brand.
Good to know
- Don't keep pressing reset. After five resets in 15 minutes the boiler shows LC and won't restart until you turn its power off and on again. Ideal's lists also give L5 for too many resets, and describe L5 elsewhere as a problem with the return. Either way, turn the power off at the wall (the fused spur) for a couple of seconds, then back on.
- Ideal says the pressure gauge should read between 1 and 1.5 bar.
- F7 means the voltage to the boiler may be too low. Ideal says to have a local electrician inspect your home's electrics.
- If the boiler is under warranty, contact Ideal first. Otherwise, use a Gas Safe registered engineer.
Official help pages
- Ideal Heating: what does my boiler fault code mean
- Ideal Heating: boiler fault codes, page 2
- Ideal Heating: Logic Combi 24, 30 and 35 troubleshooting guide
- Ideal Heating: boiler faults FAQs
Every code page links the exact pages it was checked against. Last reviewed October 2026.
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