Sime iQE Simplicity 20T Fault codes & diagnostics

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

Regular Natural Gas 20 kW 2012 onwards Discontinued
GC Number 41-283-35
Download the Sime iQE Simplicity 20T manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 14 High
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-283-35 Simplicity 20T 2012–present
Just want the most common Sime iQE Simplicity 20T faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 15 documented codes

Tap any card for details

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 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
ALL 29

Your boiler has encountered a specific internal technical error that requires a professional engineer to diagnose and reset.

High Engineer only £100-£250

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring connection harness

Related codes

Full explanation for ALL 29
ALL01

Your boiler has failed to ignite, which means it cannot provide any heating or hot water until it is reset or repaired.

High DIY-safe £100-£350

What to check first

  1. Check that your gas pre-payment meter (if you have one) has credit.
  2. Ensure that the gas supply valve to the boiler is open.
  3. Press and hold the 'R' or 'Reset' button for a few seconds to try and restart the sequence.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ALL01
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
ALL03

Your boiler has too much water inside it, causing the internal pressure to rise to an unsafe level.

Emergency DIY-safe £0-120

What to check first

  1. Check that the silver filling loop taps underneath the boiler are tightly closed.
  2. Locate a radiator bleed valve and use a key to slowly release water into a container.
  3. Monitor the boiler pressure gauge until it drops back down to between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for ALL03
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
ALL07

Your boiler has experienced an ignition failure and cannot start up to provide heat or hot water.

High DIY-safe £100-280

What to check first

  1. Check that your gas pre-pay meter has credit (if applicable).
  2. Ensure other gas appliances in your home, like a hob, are working correctly.
  3. Press the Reset button (control key 2) on the boiler panel to attempt a restart.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for ALL07
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
ALL10

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 ALL10