L4Ideal
Ideal L4: what it means on your model
Checked against Ideal's own documentation: Ideal Logic Combi ESP1 installation and servicing instructions (UIN 222353) and 2 more sources. Last reviewed October 2026. How we check
Check these first, then call an engineer
L4 means different things on different Ideal models. Check the table below against your boiler's model name, which is usually on the front panel or in your user manual. Ideal's general fault code guide lists L4 as a flow thermistor fault and says to reset the boiler first.
What you can safely do
- Reset the boiler once.
Call a Gas Safe engineer if
- L4 comes back. Ideal says an engineer visit will be needed: quote the code when you call.
Find a Gas Safe engineer near you
Opens the official Gas Safe Register search.
Applies to Logic Combi (ESP1), Exclusive 2. Codes can differ between models, so check your manual.