Common problems guide

The most common Potterton Promax SL 12 Heat ErP problems

The faults most likely to send a Potterton Promax SL 12 Heat ErP into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

The 6 most common faults

01

PCB Fault Engineer

Replace PCB.

Full guide for PCB Fault

02

DRY-FIRE Engineer

Flow & Return reversed, system not full of water, or pump fault.

Full guide for DRY-FIRE

03

IGNITION LOCKOUT Engineer

No gas at gas valve inlet, blocked flue, condensate trap blocked, damaged spark/flame probe, or burner blocked.

Full guide for IGNITION LOCKOUT

04

OVERHEAT LOCKOUT Engineer

Flow pipe stat fault, fan stat fault, faulty thermistor, or combustion chamber door seal damaged.

Full guide for OVERHEAT LOCKOUT

05

FAN LOCKOUT Engineer

Fan fault or fan PCB wiring fault.

Full guide for FAN LOCKOUT

06

THERMISTOR Engineer

Thermistor resistance out of range or wiring fault.

Full guide for THERMISTOR

Call a Gas Safe engineer if…

You can smell gas or see signs of a leak
The Potterton shows an Emergency or High severity code
The boiler keeps locking out after repeated resets
You've tried the DIY checks and the fault hasn't cleared
There's visible water leaking from the boiler
The flame is yellow or orange instead of blue

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See the full 6-code list for the Potterton Promax SL 12 Heat ErP