High
Flash On On on Potterton Promax Heat Only

Your boiler's central control computer has encountered a critical error and is unable to operate correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

PCB Fault. Replace PCB.

From this model's manual
Verified against the Potterton/Potterton Promax He Store installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like Flash On On: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

All 24 fault codes on the Promax Heat Only

Seeing a different code? Every code this model can display, in one place.

Flash Flash OnFlash Off FlashFlash Off OnFlash On FlashIgnition LockoutLights: Flash Flash OnLights: Flash Off FlashLights: Flash Off OnLights: Flash On FlashLights: Flash On OnLights: Off Off OffLights: On Flash FlashLights: On Off FlashLights: On On FlashNo Switched LiveOn Flash FlashOn Flash OnOn Off FlashOn Off OnOn On FlashOn On OnOverheat LOCKOUTPCB Fault

Related guides you might find useful

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →