B4 Low

Ideal B4 Fault Code

The Ideal B4 fault code means: your boiler is currently running at a low power level to maintain heat efficiently, which is a normal status indicator rather than a breakdown.. It appears on 1 Ideal model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Feed to 1st stage operating indicator from burner low fire control. Indicates low fire in operation.

DIY fix possible

Check if the heating or hot water is reaching the desired temperatureObserve the display to see if the code changes as demand increasesNo action is required as this is an operational status message

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Ideal models that show the B4 fault code

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

Source

Ideal B4 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 27 April 2026