Overheat Lockout 3/4 High

Ideal Overheat Lockout 3/4 Fault Code

Also written as OVERHEATLOCKOUT34 — same fault.

The Ideal Overheat Lockout 3/4 fault code means: your boiler has switched itself off because it has become too hot internally, usually because water isn't flowing through the system properly.. It appears on 1 Ideal model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Overheat lockout (screen 3 of 4) — check radiator and boiler valves are open
Typical repair cost £80-250 (including labour)

DIY fix possible

Check that all radiator valves (TRVs) are turned to the highest setting.Ensure the blue-handled isolation valves underneath the boiler are in the 'open' position (pointing towards the boiler).Press the 'Restart' button on the front control panel.Check the boiler pressure gauge is between 1.0 and 1.5 bar.

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Ideal models that show the Overheat Lockout 3/4 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ideal Overheat Lockout 3/4 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026