Potterton Assure 25 Combi Fault codes & diagnostics

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

Combi Natural GasLPG 2017-present
GC Numbers 47-393-5847-393-70
Download the Potterton Assure 25 Combi manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

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Each cell = one fault code. Hover to identify.
16 High 4 Medium
Fault codes

All 20 documented codes

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09

Your boiler has encountered a general operational fault that requires a simple reset or further investigation by an engineer to get running safely again.

High DIY-safe £90-250

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Potterton Assure boiler.
  2. Hold the reset button for about 3 to 5 seconds and release it.
  3. Wait to see if the boiler fires up normally; if the code returns immediately, do not keep resetting it.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Air pressure switch

Related codes

Full explanation for 09
15

Your boiler has temporarily stopped working as a safety precaution and needs to be reset, or it is experiencing an internal sensor error.

High DIY-safe £90-200

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Potterton Assure.
  2. Hold the reset button for approximately 3 to 5 seconds and release it.
  3. Wait to see if the boiler fires up normally; if the code returns immediately, do not keep resetting it.

Parts commonly replaced

  • NTC Thermistor
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 15
20

Your boiler has detected an internal error that requires a professional engineer to safely diagnose and resolve.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board
  • Wiring harness
  • Sensor

Related codes

Full explanation for 20
28

Your boiler has stopped working because it has detected an internal fault that requires a Gas Safe engineer to inspect and test the electrical and gas components.

High Engineer only £150-350

Parts commonly replaced

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

Related codes

Full explanation for 28
40

Your boiler has detected an internal system fault that requires a Gas Safe registered engineer to inspect and diagnose safely.

High Engineer only £100-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Pressure Switch
  • Wiring Harness

Related codes

Full explanation for 40
103

Your boiler has lost communication with an optional safety device fitted to the system, causing it to pause operation.

Medium Engineer only £90-180

Parts commonly replaced

  • Safety Assist accessory module
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 103
104

Your boiler has detected an issue with an optional safety monitoring device attached to the system.

Medium Engineer only £90-180

Parts commonly replaced

  • Safety Assist module
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 104
107

Your boiler has detected an issue with an optional safety monitoring device attached to the system.

Medium Engineer only £90-180

Parts commonly replaced

  • Safety Assist module
  • Wiring harness
  • PCB

Related codes

Full explanation for 107
109

Your Potterton boiler has detected a general internal fault that requires a Gas Safe registered engineer to inspect and diagnose properly.

High Engineer only £100-£250

Parts commonly replaced

  • PCB
  • Wiring harness
  • Pressure sensor

Related codes

Full explanation for 109
110

Your boiler has temporarily stopped working as a safety precaution and needs to be reset, or it may be experiencing a deeper internal issue.

High DIY-safe £100-250

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Potterton Assure.
  2. Hold the reset button for approximately 3 to 5 seconds.
  3. Wait a moment to see if the boiler fires back up; do not repeatedly reset if the fault immediately returns.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • NTC Thermistor
  • Air Pressure Switch

Related codes

Full explanation for 110
Showing 11–20 of 20
118

Your boiler has detected an issue with the water pressure or flow inside the system and has safely shut down to prevent damage.

High Engineer only £90-200

Parts commonly replaced

  • Pressure sensor
  • Circulating pump
  • Water pressure switch

Related codes

Full explanation for 118
125

Your boiler is locking out because water is not flowing properly through the heating system inside the boiler.

High Engineer only £150-£350

Parts commonly replaced

  • Automatic bypass valve
  • Circulating pump
  • Plate heat exchanger

Related codes

Full explanation for 125
128

Your boiler has stopped because the flame inside has gone out and it cannot get it to stay lit.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 128
130

Your boiler has detected an internal safety or sensor issue that requires a qualified engineer to investigate and resolve.

High Engineer only £150-300

Parts commonly replaced

  • PCB
  • Wiring harness
  • Temperature sensor

Related codes

Full explanation for 130
133

Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 133
134

Your boiler has stopped working because it cannot light the internal flame to provide heat or hot water.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

Full explanation for 134
135

Your boiler has stopped working because it cannot light the gas flame needed to produce heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)

Related codes

Full explanation for 135
160

Your boiler has stopped working because it cannot detect that the internal fan is spinning properly to safely clear exhaust gases.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 160
321

Your boiler has detected an internal system fault that requires professional inspection by a Gas Safe engineer.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 321
384

Your boiler has temporarily locked out due to a technical internal error and needs a reset, or possibly a check by a professional if the problem keeps returning.

Medium DIY-safe £100-250

What to check first

  1. Locate the reset button or turn the mode dial to the reset position on your Potterton Assure.
  2. Hold the reset button for about 3 to 5 seconds and release it.
  3. Wait to see if the boiler fires up normally; if the code returns immediately, do not keep resetting it.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for 384
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