Ideal boiler fault codes, explained
If your Ideal boiler has stopped and is showing a code, this guide will tell you what it means, whether there is anything safe you can do yourself, and when you need a Gas Safe engineer. These codes apply to the Ideal Logic, Logic+, Vogue, and related ranges.
Before you do anything else: if you can smell gas, do not touch the boiler. Leave the building, leave the door open, and call the National Gas Emergency line on 0800 111 999.
Quick fault-code reference
| Code | What it means | What to do |
|---|---|---|
| F1 | Low water pressure | Check the pressure gauge. If it reads below 1 bar, re-pressurise using the filling loop (see guide below). If it keeps dropping, call an engineer. |
| F2 | Flame loss | The boiler ignited but the flame cut out. Check other gas appliances are working. If they are, try one reset. If the code returns, call a Gas Safe engineer. |
| F3 | Fan fault | The boiler’s flue fan has a problem. Do not reset repeatedly. Call a Gas Safe engineer. |
| F4 | Flow thermistor fault | A sensor has failed. Requires a Gas Safe engineer. |
| F9 | PCB fault | The printed circuit board is unconfigured or faulty. Requires a Gas Safe engineer. This can be costly; check your warranty first. |
| L1 | Flow temperature overheat / no circulation | The boiler overheated or detected no water flow. Try one reset. If the code returns, call a Gas Safe engineer. |
| L2 | Ignition lockout | The boiler tried to light and failed. Check the condensate pipe has not frozen (in cold weather). Try one reset. If it locks out again, call a Gas Safe engineer. |
| L5 | Too many resets | The boiler has been reset five or more times within roughly 15 minutes and has locked itself out permanently. Do not reset again. Call a Gas Safe engineer to find the underlying fault. |
| L6 | False flame lockout | The boiler detected a flame signal when it should not have. Switch off the boiler and call a Gas Safe engineer. |
| FU | Large temperature differential | The flow and return temperatures differ by more than 50 degrees Celsius, often because isolation valves are closed. Check valves are fully open; if the code persists, call an engineer. |
F1 — low water pressure: what you can do
F1 is the most common Ideal fault code and it is often something you can clear yourself. The boiler needs to sit at around 1 to 1.5 bar when the heating is off. If the pressure has dropped below 1 bar, here is how to top it up:
- Find the filling loop — a short braided hose under or near the boiler connecting two valves.
- Open both valves slowly and watch the pressure gauge climb.
- Once the gauge reads around 1.2 to 1.5 bar, close both valves.
- Press the reset button once and wait for the boiler to restart.
If the pressure is fine but F1 keeps appearing, or if the pressure drops again within a few days, there is a leak somewhere in the system and you need an engineer.
L2 — ignition lockout: common causes
L2 is the second most common Ideal fault. The boiler tried to light but could not detect a stable flame. Common reasons include:
- Frozen condensate pipe. In cold weather the plastic drain pipe running outside can ice up. Gently warming the external section with a hot water bottle (not boiling water) often clears it.
- Gas supply issue. Check whether your hob or other gas appliances are working. If nothing gas-powered is working, your supply may be interrupted, check your meter credit if you have a prepayment meter.
- One-off ignition glitch. Try a single reset. If the boiler fires and holds, it may have been a temporary issue.
If L2 returns after one reset, stop. Repeated ignition attempts without resolving the cause can wear out ignition components faster.
L5 — the repeated-reset lockout
L5 appears when the boiler has detected five or more resets within about 15 minutes. It is a safety feature, not a new fault. The actual fault is usually F1 (low pressure) or L2 (ignition) happening repeatedly. A Gas Safe engineer will read the fault history, find what triggered the cycle, and fix it at source.
The one-reset rule
With any Ideal lockout, one reset is reasonable. Press the reset button, wait for the boiler to go through its start sequence, and see if it settles. If it locks out again, stop. Every unsuccessful reset sends the boiler through an ignition or pressure cycle that can accelerate wear and, in some faults, introduce risk. The code plus one failed reset gives an engineer everything they need to diagnose the problem quickly.
Safety: what never to do yourself
- Never remove the boiler casing.
- Never touch the gas valve, burner, or flue.
- Never reset the boiler more than once without clearing the fault.
- If there is any smell of gas, do not use any switches or appliances. Leave and call 0800 111 999.
Gas appliances must only be worked on by a Gas Safe registered engineer. It is a legal requirement, not just good advice.
Still showing a fault code?
BASI Heating is Gas Safe registered (no. 623525) and has been repairing boilers across Yorkshire for over 30 years. We repair all makes, including Ideal, and our same-day boiler repair service starts from £80 for the first hour, fixed pricing, no call-out fee surprises.
We cover the whole of Yorkshire, including:
If the fault code has cleared but the boiler has not been serviced recently, an annual service catches small problems before they become lockouts.