Ideal boiler fault codes
Ideal boilers show a letter and a number, such as F1 or L2. Some codes mean different things on different Ideal models, so each page tells you which model the meaning applies to. If in doubt, check your user guide.
Before you call anyone
F1 (low pressure) and L2 (ignition lockout) mean the same on every Ideal guide we checked, and they are the codes Ideal owners search for most. For L2, Ideal's advice is to check the condensate pipe and your gas supply before calling anyone.
| Code | What it means | Models | Can you fix it? |
|---|---|---|---|
| F1 | Low water pressure. | Logic Combi (ESP1), Exclusive 2 | Usually yes |
| L2 | Ignition lockout: the boiler failed to light. | Logic Combi (ESP1), Exclusive 2 | Checks first |
| L1 | No water flow or overheat, or a condensate pipe blockage, depending on the model. | Logic Combi (ESP1), Exclusive 2 | Checks first |
| F2 | Flame loss on Ideal Logic boilers (overheat or no water flow on the Exclusive 2). | Logic Combi (ESP1), Exclusive 2 | Checks first |
| L5 | Return thermistor fault (Logic) or too many resets (Exclusive 2). | Logic Combi (ESP1), Exclusive 2 | Checks first |
| F3 | Fan fault (Ideal Logic). | Logic Combi (ESP1) | Checks first |
| F4 | Flow thermistor fault (Ideal Logic). | Logic Combi (ESP1) | Checks first |
| C0 | BCC activation fault. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| C2 | BCC chip fault. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| DU | Diverter valve in mid-position for service. | Ideal boilers (Ideal's general fault code guide) | Usually yes |
| F0 | No water flow thermistor. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| F5 | Return thermistor fault. | Logic Combi (ESP1) | Checks first |
| F6 | Outside sensor fault. | Logic Combi (ESP1) | Checks first |
| F7 | Low mains voltage. | Ideal boilers (Ideal's general fault code guide) | No, engineer only |
| FA | Flow and return pipes are reversed. | Ideal boilers (Ideal's boiler faults FAQ) | No, engineer only |
| FD | No water flow. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| Fn | Flame loss. | Logic Combi (ESP1) | Checks first |
| FU | Flow and return temperature difference of more than 50°. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| L3 | No water flow. | Ideal boilers (Ideal's general fault code guide) | Checks first |
| L4 | Varies by model: flow thermistor fault (Logic Combi (ESP1)); flame loss (Exclusive 2). | Logic Combi (ESP1), Exclusive 2 | Checks first |
| L6 | Varies by model: false flame lockout (Logic Combi (ESP1)); fan fault (Exclusive 2). | Logic Combi (ESP1), Exclusive 2 | Checks first |
| Ln | Flame loss. | Logic Combi (ESP1) | Checks first |
| SE | Service interval timer. | Ideal boilers (Ideal's general fault code guide) | Checks first |
Sources
- Ideal Heating: what does my boiler fault code mean?
- Ideal Heating: Logic Combi troubleshooting guide
- Ideal Heating: Exclusive 2 user guide
- Ideal Logic Combi ESP1 installation and servicing instructions (UIN 222353)
- Ideal Heating: what does my boiler fault code mean? (page 2)
- Ideal Heating: boiler faults FAQs
Last reviewed October 2026. Spotted something that doesn't match your manual? Email hello@boilercodes.co.uk and we'll check it. How we check