L5Ideal
Ideal L5: return thermistor fault (Logic) or too many resets (Exclusive 2)
Checked against Ideal's own documentation: Ideal Logic Combi ESP1 installation and servicing instructions (UIN 222353) and 3 more sources. Last reviewed October 2026. How we check
Check these first, then call an engineer
L5 means different things on different Ideal models. On the Logic Combi it's a return thermistor fault, which Ideal's boiler faults FAQ describes as a problem with the return. On the Exclusive 2, and in Ideal's general fault code guide, it means the boiler has been reset too many times in a short period (five resets in 15 minutes). Ideal's advice for both is the same first step: turn the power off and on.
What you can safely do
- Turn the electrical supply to the boiler off for a few seconds, then back on, as Ideal advises.
Call a Gas Safe engineer if
- The boiler still won't work. Contact Ideal if it 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), Exclusive 2. Codes can differ between models, so check your manual.