Sime iQE Simplicity 20T Fault codes & diagnostics

11 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Regular Natural Gas 2012-present
GC Number 41-283-35
Download the Sime iQE Simplicity 20T user guideThe manufacturer's user instructions (PDF). We don't hold the installation and service manual for this model yet. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
11 High
Fault codes

All 11 documented codes

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ALL 06

Your boiler has failed to ignite or detect a flame, causing it to shut down for safety.

High DIY-safe £120-350

What to check first

  1. Press the Reset button (control key 2) to attempt a restart
  2. Check that your gas meter has credit and the gas emergency control valve is open
  3. Check if other gas appliances, like a cooker, are working correctly

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensing probe
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ALL 06
ALL 10

Your boiler has detected low water pressure in the system, which means it cannot circulate water safely or effectively.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually two blue levers or a braided hose) under the boiler.
  2. Slowly open the valves until you hear water flowing and the pressure gauge reaches between 1.0 and 1.5 bar.
  3. Close both valves completely and press the reset button on the control panel.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for ALL 10
ALL 13

Your boiler has experienced a temporary software or operational glitch and needs a manual restart to try and clear the error.

High DIY-safe £80-180

What to check first

  1. Locate the control panel on the front of the boiler.
  2. Press the button labeled with the 'Reset' or '2' icon.
  3. Wait for the boiler to complete its startup sequence.
  4. If the code returns immediately, contact a Gas Safe engineer.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Control Interface

Related codes

Full explanation for ALL 13
ALL 14

Your boiler has detected an internal electronic error or a serious signal failure that requires a professional inspection to diagnose.

High Engineer only £120-£400

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for ALL 14
ALL 15

Your boiler has detected an internal communication failure between its electronic control boards, meaning it cannot operate safely and has shut down.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Display PCB
  • Wiring Harness

Related codes

Full explanation for ALL 15
ALL 20

Your boiler has encountered a generic system failure that requires a professional diagnosis to prevent further damage.

High Engineer only £100-350

Parts commonly replaced

  • Main PCB
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for ALL 20
ALL02

Your boiler has stopped working because the water pressure is too low for it to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Slowly open the valve or valves on the filling loop until you hear water flowing.
  3. Watch the pressure gauge on the boiler until it reaches between 1.0 and 1.5 bar, then close the valves fully.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for ALL02
ALL04

Your boiler has detected an internal electronic or sensor problem and has shut down as a safety precaution.

High Engineer only £120-£350

Parts commonly replaced

  • Main PCB
  • Temperature Sensor
  • Wiring Loom

Related codes

Full explanation for ALL04
ALL05

Your boiler has detected a technical fault that has caused it to shut down for safety, and it requires a professional inspection to identify the internal cause.

High Engineer only £100-350

Parts commonly replaced

  • Main PCB
  • Fan
  • Air Pressure Switch

Related codes

Full explanation for ALL05
ALL08

Your boiler has detected an internal electronic error or a serious combustion issue that requires a professional inspection to fix.

High Engineer only £120-350

Parts commonly replaced

  • Main PCB
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for ALL08
ALL09

Your boiler has stopped working because water is not flowing through the system correctly.

High DIY-safe £100-£280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the blue handled isolation valves under the boiler are in the open position
  3. Check if the system pressure is too low and top up if necessary

Parts commonly replaced

  • Circulation pump
  • Internal water filter
  • Flow temperature sensor

Related codes

Full explanation for ALL09
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