BoilerFaultCodesPotterton E20 Fault Code
The Potterton E20 fault code means: your boiler thinks a flame is present even though it hasn't turned the gas on, usually caused by a blocked drain or a faulty sensor.. It appears on 14 Potterton models in our database.
Technical description: Flame detected with closed gas valve. Check ionization probe/cable. Check condensate outlet not blocked & vent tube clear
What causes the Potterton E20 fault?
This fault occurs when the boiler's control system senses a flame internal to the unit even though it hasn't signaled the gas valve to open. The most common cause is a surge of water or moisture backing up into the combustion chamber due to a blockage in the condensate drain or a buildup of carbon on the sensing probe. In some cases, a damaged ignition lead or a failing control board can also send a false electrical signal that mimics the presence of a flame.
This fault is more common during the winter months, as freezing temperatures can cause the external condensate pipe to block with ice, forcing water back into the boiler.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Potterton models that show the E20 fault code
Click a model for the full fault code list and model-specific repair notes.
- Apollo Repair: £120-200
- Gold Combi ErP Repair: £90-160
- Gold Combi HE Repair: £90-160
- Gold HE Repair: £90-160
- Gold System ErP Repair: £120-£190
- Heatmax Combi Repair: £120-220
- Powermax HE Repair: £120-250
- Promax 15 & 24 Repair: £150-300
- Promax Combi 28 HE Plus Repair: £90-160
- Promax Combi ErP Repair: £90-160
- Promax Combi HE Plus Repair: £90-160
- Promax System ErP Repair: £100-£170
- Promax System HE Plus Repair: £90-160
- Titanium Combi Repair: £120-220
Source
Potterton E20 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 Gold Combi ErP manual (PDF)
- Potterton Gold Combi HE manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026