Common problems guide

The most common Ideal istor HE325 problems

The faults most likely to send a Ideal istor HE325 into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
9 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
L- High DIY-safe

Your boiler has switched itself off for safety and is displaying a 'lockout' status, which will be accompanied by a second flashing code to tell you exactly what is wrong.

What to try first

Check the display for the secondary flashing number or letter that follows the 'L'Press and hold the 'Reset' button for two secondsCheck if your gas credit has run out or if other gas appliances are working

Est. cost
£0-350
Parts
Ignition Electrode, Printed Circuit Board (PCB), Gas Valve
Full guide for L-
02
F- High DIY-safe

Your boiler has stopped working because it has detected a specific internal problem, which it will show by alternating the 'F' with another number or letter.

What to try first

Wait for the display to flash the number or letter following the 'F' to identify the specific fault.Try resetting the boiler by turning the mode knob to 'Reset' for two seconds and then back to the original setting.Check that your gas supply is active and your prepaid meter (if applicable) has credit.

Est. cost
£80-350
Parts
Ignition Electrode, Printed Circuit Board (PCB), Fan
Full guide for F-
03
L A High Engineer

Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent internal damage.

Est. cost
£120-250
Parts
Overheat thermostat, Primary flow sensor, Circulation pump
Full guide for L A
04
H E High Engineer

Your boiler's internal computer is experiencing a communication fault and cannot control the system correctly.

Est. cost
£250-450
Parts
Main PCB, Wiring harness
Full guide for H E
05
H9 High Engineer

Your boiler has detected that it is getting dangerously hot and has shut itself down to prevent damage.

Est. cost
£150-350
Parts
Pump, Diverter valve, Heat exchanger
Full guide for H9
06
L9 High Engineer

Your boiler has detected that it is becoming dangerously hot and has shut itself down to prevent any internal damage.

Est. cost
£150-350
Parts
Plate to plate heat exchanger, Pump, NTC thermistor
Full guide for L9
Parts most often replaced

on the Ideal istor HE325

Ignition ElectrodePrinted Circuit Board (PCB)Gas ValveFanOverheat thermostatPrimary flow sensor

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Ideal shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 9-code list for the Ideal istor HE325

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →