BoilerFaultCodesPotterton 20 Fault Code
The Potterton 20 fault code means: your boiler has stopped working because it failed to light properly or the waste water pipe is blocked.. It appears on 14 Potterton models in our database.
Technical description: Flame Failure or Blocked Condensate Drain
What causes the Potterton 20 fault?
This fault occurs when the boiler tries to light but cannot detect a stable flame, prompting the system to shut down for safety. The most common reasons are a lack of gas supply, a dirty sensing probe that can't 'see' the flame, or a blockage in the waste water pipe that causes water to back up into the heat exchanger. In many cases, it is simply a sign that the components responsible for the spark or flame monitoring have worn out.
This fault is significantly more common during freezing winter temperatures, as the external condensate pipe can freeze, causing water to back up and prevent the boiler from lighting.
DIY fix possible
Check that your gas pre-pay meter hasn't run out of credit.Inspect the white plastic pipe (condensate pipe) outside to see if it is frozen or blocked.Attempt to reset the boiler by turning the control knob to 'R' for five seconds.
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Potterton models that show the 20 fault code
Click a model for the full fault code list and model-specific repair notes.
- Apollo Repair: £120-200
- Assure Repair: £150-300
- ASSURE 30 COMBI LPG
- Gold Combi HE Repair: £180-350
- Performa System HE Repair: £100-£280
- Promax Combi 28 HE Plus Repair: £90-160
- Promax Combi HE Plus Repair: £90-160
- Promax Ultra Combi ErP Repair: £120-200
- Titanium Combi Repair: £150-300
- Ultra 12 System
- Ultra 15 System
- Ultra 18 System
- Ultra 24 System
- Ultra 28 System
Source
Potterton 20 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
- Potterton Apollo manual (PDF)
- Potterton Assure manual (PDF)
- Potterton ASSURE 30 COMBI LPG manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026