Overview
The LC fault on Ideal Logic Max and Logic Plus regular boilers means the boiler has carried out too many automatic restarts in a short period — specifically five restarts within 15 minutes — and has gone into a safety lockout. The boiler does this to protect internal components and to prevent unsafe operating conditions when a recurring fault is causing repeated shutdowns and automatic attempts to restart. This code is a symptom, not a single root cause. Common underlying reasons include repeated ignition or flame problems, intermittent gas supply, circulation issues (pump seizing, airlock or no flow), low system pressure, a blocked condensate pipe, faulty sensors or flow switch, problems with the control electronics (PCB or chip card), or an external control rapidly turning the boiler on and off (thermostat or programmer fault). Severity is moderate to high because the boiler is locked out and repeated restarts can indicate gas or safety-related failures — avoid repeatedly forcing the boiler to restart. Some basic checks and simple fixes are safe for a homeowner, but if the fault repeats or if you suspect a gas issue, you must call a Gas Safe registered engineer.
Troubleshooting Steps
Safety precautions:
- If you smell gas: do not operate switches or the boiler. Open doors/windows, leave the property and call the gas emergency number immediately.
- If the boiler is locked out, do not repeatedly attempt resets more than two or three times; this could hide an ongoing gas, electrical or safety issue.
- Do not attempt internal gas, electrical or PCB repairs yourself. Only a Gas Safe registered engineer should work on gas components.
Initial checks a homeowner can do:
1) Note exactly when LC appears (on central heating call, hot water call, immediately at power-up etc.). This information helps the engineer.
2) Check the boiler pressure gauge. With the boiler cold the pressure should usually be around 1.0–1.5 bar. If it is well below 1 bar, the system may be losing water and the boiler can cycle. If low, re-pressurise the system (see next section).
3) Check other gas appliances (hob, gas fire) to confirm you have a gas supply. If none of your gas appliances work, contact your gas supplier.
4) Check the condensate pipe (usually outside) for visible blockages or freezing in cold weather. If frozen, thaw with warm (not boiling) water.
5) Check your thermostat, programmer and any external controls or room stats for correct settings and batteries (for wireless stats). A faulty or rapidly switching external control can cause frequent restarts.
6) Listen for unusual noises when the boiler attempts to start: repeated ignition attempts, long fan spin-up, or the pump trying to run then stopping may indicate ignition, fan, or circulation faults.
Diagnostic and basic fix steps you can try:
1) Reset the boiler once using the normal reset procedure in the user manual (many guides say turn the power off then on). If the LC clears and does not recur, monitor for the problem returning. Do not keep resetting repeatedly.
2) Re-pressurise the system if pressure is low: with the boiler off and cold, open the filling loop slowly until the gauge reaches about 1.0–1.5 bar, then close the filling loop and fully isolate it. After repressurising, reset the boiler. If pressure drops again, do not continue topping up repeatedly — call an engineer for a leak check.
3) Bleed radiators to remove trapped air which can cause poor circulation. After bleeding, check and top up pressure again if needed.
4) Inspect the condensate outlet/pipework for blockages or freezing. Clear any visible debris or thaw frozen condensate using warm water. If condensate blockage is suspected and clearing does not help, call an engineer.
5) Check external controls: set the programmer to call the boiler manually for hot water only and see whether LC occurs on that demand. Try isolating the room thermostat or turning off timers temporarily to see if the fault stops — if the boiler runs normally with external controls disconnected, the problem may be with the thermostat/wiring.
6) If you suspect the pump is seized (no flow noise, radiators not heating despite boiler firing), do not dismantle the pump. You can try briefly running the system demand and listening; if pump is the likely cause, call an engineer.
When to call a professional:
- If LC returns after basic checks and a reset, or if the boiler locks out repeatedly.
- If you find low or rapidly dropping pressure that you cannot trace, or if there is visible leakage.
- If condensate or circulation checks don’t stop the lockouts, or you suspect ignition, flame, fan, PCB or gas valve faults.
- If you are unsure or uncomfortable performing any of the checks above.
What to tell the engineer:
Provide the exact fault code (LC), how often it has occurred, what demand triggered it (CH or DHW), the boiler pressure reading, whether other gas appliances are working, whether the condensate pipe was blocked/frozen, and any recent work or power cuts. That helps the Gas Safe engineer diagnose and fix the underlying cause quickly.
Final note:
LC is a safety lockout. Simple user checks (reset, repressurise, clear condensate, check controls) are acceptable, but persistent or unclear faults must be investigated and repaired by a qualified Gas Safe registered heating engineer. Do not attempt gas or PCB repairs yourself.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Ideal Logic Max & Logic Plus Regular Boiler.