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BoilerCodes
F4
Ideal fault code

Ideal F4: flow thermistor fault (Ideal Logic)

Check these first, then call an engineer

On Ideal Logic boilers, F4 (and L4) means a problem with the sensor that measures the temperature of water leaving the boiler. Ideal suggests a restart first. On the Exclusive 2, L4 means flame loss instead, and Ideal says F4 needs Ideal or a Gas Safe engineer.

What you can safely do

  1. Restart the boiler once.

Call a Gas Safe engineer if

  • The code comes back after a restart. Contact Ideal if the boiler is under warranty, or a Gas Safe registered engineer.
Find a Gas Safe engineer near you Opens the official Gas Safe Register search.

Applies to: Logic Combi (ESP1). Codes can differ between models, so check your manual.

What F4 means on each Ideal model

From Ideal's own fault tables. Your model name is usually on the front of the boiler or in the user manual.

ModelMeaning
Logic Combi (ESP1)Flow thermistor fault

Common questions about Ideal F4

Is F4 the same as L4?

On Ideal Logic boilers, Ideal groups F4 and L4 together as a flow thermistor fault. On the Exclusive 2 they are different: L4 is flame loss.

Nearby Ideal codes

F1L2L1F2L5F3C0C2F0F5F6F7

See all 19 Ideal codes

Sources