E85 Boiler Fault Code: What It Means on Every Brand

The E85 fault code appears on 2 boiler brands — Baxi and Potterton — and on all of them it points to the same kind of problem. The details still differ by brand (thresholds, sub-codes, reset procedure), so use the table below to jump to the page for your boiler.

Lockout — engineer likely 2 brands use this code

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What E85 means	Severity	DIY?
BBaxi	The E85 code on a Baxi boiler signals a breakdown in communication between the boiler's internal components. Full guide →	Lockout — engineer likely	No
PPotterton	The E85 code on a Potterton boiler signals that the printed circuit board (PCB) has triggered a full safety lockout. Full guide →	Lockout — engineer likely	No

E85 brand by brand

Baxi E85

The E85 code on a Baxi boiler signals a breakdown in communication between the boiler's internal components. The PCB (Printed Circuit Board) acts as the control hub of the boiler — every sensor, pump, valve, and ignition component sends and receives signals through it. When this communication chain breaks down, the boiler locks out as a precaution, preventing it from operating until the issue is identified and resolved. E85 sits within a wider family of Baxi communication fault codes (E83, E84, E85, E86, E87), each pointing to a slightly different communication path failing; E85 specifically indicates the PCB is not receiving the expected signals from one or more connected components. Because the fault is electrical in nature, it almost always requires a Gas Safe registered engineer to diagnose and repair.

Causes, fixes & costs for Baxi E85 → · All Baxi codes

Potterton E85

The E85 code on a Potterton boiler signals that the printed circuit board (PCB) has triggered a full safety lockout. The PCB is the electronic brain of your boiler — it orchestrates every component from ignition through to pump control. When the board detects an internal fault serious enough to compromise safe operation, it shuts everything down and displays E85 to alert you. This sits within the E83–E87 family of Potterton fault codes, all of which relate to the PCB or communication between the board and external controllers such as a room thermostat. E83 and E84 tend to indicate lighter communication errors, while E85 specifically points to a more significant internal board failure that has forced a hard lockout. E86 and E87 similarly reflect controller communication breakdowns. If your display shows E85, the boiler will not restart until the underlying fault is resolved.

Causes, fixes & costs for Potterton E85 → · All Potterton codes

Frequently asked questions

Is the E85 fault code the same on every boiler?

Broadly, yes — on Baxi and Potterton the E85 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.

Can I fix a E85 fault myself?

Not usually. On every brand listed, E85 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a E85 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.