Potterton Suprima Fault codes & diagnostics

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

Gas 2001 onwards Discontinued
Choose your boiler type

The Suprima range comes in 4 types

Pick the one you have. The fault codes, GC numbers and manual differ by type.

30L 1 codes · 1 GC number 40L 1 codes · 1 GC number 50L 1 codes · 1 GC number 60L 1 codes · 1 GC number
Each model has its own manual A family spans several manuals, one per model or generation. Pick your model above and its page has the manual its fault codes were read from.

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 5 High 3 Low
Just want the most common Potterton Suprima faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 9 documented codes

Tap any card for details

Blocking

Your boiler has temporarily stopped working because it has detected an issue with the electricity supply frequency or an internal safety switch.

High Engineer only £150-300 Shared across the Suprima range

Parts commonly replaced

  • Air Pressure Switch
  • PCB

Related codes

Full explanation for Blocking
Earth Fault

Your boiler has detected that the internal electrical wires for the live and neutral supply have been reversed during installation or a recent repair.

Emergency Engineer only £80-150 Shared across the Suprima range

Parts commonly replaced

  • Fused Spur
  • Internal Wiring
Full explanation for Earth Fault
Ext. Call for Heat (Boiler set to STNDBY, Temp. Control set to 'O' Off)

Your boiler is currently switched off or set to standby mode while your heating controls are still asking it to provide heat.

High DIY-safe Shared across the Suprima range

What to check first

  1. Check the temperature control dial on the front of the Potterton Suprima and turn it up from the 'O' (Off) position.
  2. Ensure the boiler mode switch is moved from 'STNDBY' to 'ON' or 'RUN'.
  3. Check your external room thermostat or programmer to see if it is correctly scheduled and calling for heat.
Full explanation for Ext. Call for Heat (Boiler set to STNDBY, Temp. Control set to 'O' Off)
Ext. Call for Heat (STNDBY switch to ON, Temp. Control set to Max.)

Your boiler is currently on standby waiting for a signal for heating or hot water, which is a normal operational state rather than a fault.

Low DIY-safe Shared across the Suprima range

What to check first

  1. Check that your room thermostat or heating programmer is turned up and set to schedule an active heating period.
  2. Turn the boiler's internal or external temperature controls up to maximum to trigger a call for heat.
  3. If the heating still does not fire up, try resetting the boiler using its main power switch or reset button.
Full explanation for Ext. Call for Heat (STNDBY switch to ON, Temp. Control set to Max.)
Lockout

Your boiler has temporarily stopped working for safety reasons, meaning you currently have no heating or hot water.

High DIY-safe £100-250 Shared across the Suprima range

What to check first

  1. Check your gas supply by ensuring other gas appliances, like your cooker, are working.
  2. Check that your prepay meter (if you have one) has credit.
  3. Locate the reset button on your Potterton Suprima and press it firmly for 5 seconds to see if the boiler fires back up.

Parts commonly replaced

  • PCB
  • Ignition Lead
  • Gas Valve

Related codes

Full explanation for Lockout
Mains ON Only

Your boiler has detected an internal fault that has caused it to stop heating your home and hot water for safety reasons.

High Engineer only £150-300 Shared across the Suprima range

Parts commonly replaced

  • PCB
  • Ignition lead
  • Gas valve
Full explanation for Mains ON Only