Potterton Promax Fault Codes

The Potterton Promax is the brand's long-running mainstream range — combi, system and heat-only (HE and later generations) — and, Potterton being part of the same Baxi Heating stable, it shares the group's E-code fault language wholesale: E119 low system pressure, E133 gas/ignition lockout, E110 overheat, E125 circulation and the familiar supporting cast. Promaxes were installed in enormous numbers, particularly heat-only versions replacing old floor-standing and back boilers in system conversions — so many run alongside older radiator circuits, tanks and external controls. That context matters diagnostically: the boiler's code tells you the boiler's complaint, but the cause often lives out in the ageing system around it. Each code below links to its full cause-and-fix page.

Where Promax fault codes appear

The Promax shows E-prefixed codes on its digital display when faults trip. On heat-only installations with external programmers and valves, confirm the fault is genuinely at the boiler — a silent boiler awaiting a call from a failed external control shows no code at all.

Resetting a Potterton Promax

Press or turn the reset control briefly; the boiler clears and retries. E119 wants the system topped up to 1–1.5 bar via the filling loop first. E133 on a frosty morning: check and thaw the condensate pipe with warm water before resetting — the classic winter fix across the whole Baxi-group fleet.

Common Promax problems

Promax installations mostly log E119 pressure loss, E133 winter ignition lockouts, and — reflecting the older systems many serve — circulation and overheat codes driven by sludge, tired pumps and decades-old pipework. A system clean, magnetic filter and inhibitor rejuvenate these installations remarkably; the boiler is often the healthiest component present.

Most common Promax fault codes

See all Potterton fault codes →

Last reviewed 25 August 2026.