E41 Boiler Fault Code: What It Means on Every Brand

The E41 fault code appears on 3 boiler brands — Andrews, Keston and Ravenheat — 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 3 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 E41 means	Severity	DIY?
AAndrews	The E41 code on Andrews boilers signals that the control board has detected the heating flow water temperature is outside its accepted range — either running too high or too low. Full guide →	Lockout — engineer likely	No
KKeston	The E41 code indicates that the boiler's fascia (the front control panel) and the main control box (PCB) have lost communication with each other. Full guide →	Lockout — engineer likely	No
RRavenheat	The E41 code on a Ravenheat boiler means the boiler's control board has detected an unexpectedly large difference between the temperature of water leaving the boiler (the flow) and the… Full guide →	Lockout — engineer likely	No

E41 brand by brand

Andrews E41

The E41 code on Andrews boilers signals that the control board has detected the heating flow water temperature is outside its accepted range — either running too high or too low. The boiler monitors flow temperature continuously via an NTC (Negative Temperature Coefficient) thermistor, a small sensor whose electrical resistance changes in step with temperature. When the PCB receives a reading that falls outside safe parameters, it triggers E41 and locks out to protect the appliance. The fault can stem from a genuine overtemperature or undertemperature condition in the water circuit, or it can be triggered by a faulty sensor or wiring fault that is feeding the PCB incorrect data. Andrews is a commercial and industrial specialist within the Baxi Group, and fault code definitions can vary between models — always cross-reference with the installation manual for your specific unit if you have it to hand.

Causes, fixes & costs for Andrews E41 → · All Andrews codes

Keston E41

The E41 code indicates that the boiler's fascia (the front control panel) and the main control box (PCB) have lost communication with each other. When this breakdown in the internal data link occurs, the boiler locks out completely and will not attempt to restart on its own — you must press the Reset button to try to clear it. Note that error code E99 on Keston boilers points to the same underlying fault and should be diagnosed in exactly the same way as E41.

Causes, fixes & costs for Keston E41 → · All Keston codes

Ravenheat E41

The E41 code on a Ravenheat boiler means the boiler's control board has detected an unexpectedly large difference between the temperature of water leaving the boiler (the flow) and the temperature of water returning to it (the return). Every Ravenheat boiler uses a pair of NTC thermistors to continuously monitor these two temperatures. Under normal operation, the gap between flow and return sits within an acceptable band; when that gap exceeds the boiler's programmed threshold — whether due to a faulty sensor, restricted water circulation, or a blocked heat exchanger — the boiler locks out and displays E41 as a safety measure.

Causes, fixes & costs for Ravenheat E41 → · All Ravenheat codes

Frequently asked questions

Is the E41 fault code the same on every boiler?

Broadly, yes — on Andrews, Keston and Ravenheat the E41 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 E41 fault myself?

Not usually. On every brand listed, E41 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 E41 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.