Ideal Heating · Logic Code Combi ESP1
L5 / F5Return thermistor fault
This code applies to Logic Code Combi ESP1 26, Logic Code Combi ESP1 33, Logic Code Combi ESP1 38. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- No internal homeowner repair is safe for this fault.
- A single reset may be tried only where the model's user manual allows it.
- Arrange an engineer if the code remains or returns.
How an engineer may fix it
Test the relevant sensor or thermistor, its position, resistance, plug and wiring; repair the connection or replace the failed sensor and verify operation.
Manufacturer source: Ideal Heating — Logic Code Combi ESP1 Installation & Servicing (UIN 222364 A04). Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.