E42 Boiler Fault Code: What It Means on Every Brand

The E42 fault code appears on 3 boiler brands — Andrews, Ravenheat and Warmflow — 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 E42 means	Severity	DIY?
AAndrews	The E42 code on Andrews water heaters and boilers indicates that the control board has detected an abnormal temperature reading on the water returning from your heating circuit — the… Full guide →	Lockout — engineer likely	No
RRavenheat	E42 on a Ravenheat boiler belongs to the E42–E44 fault group, which Ravenheat's documentation describes as a 'different temperature' error — the control board is comparing readings from… Full guide →	Lockout — engineer likely	Some checks
WWarmflow	The E42 code appears on certain Warmflow Agentis combination boiler models and, based on the fault numbering pattern used across the Warmflow range, most likely indicates a domestic hot… Full guide →	Lockout — engineer likely	No

E42 brand by brand

Andrews E42

The E42 code on Andrews water heaters and boilers indicates that the control board has detected an abnormal temperature reading on the water returning from your heating circuit — the pipework bringing cooled water back to the boiler after it has passed through your radiators or underfloor heating. The return temperature is either too high or too low compared to what the system expects, so the boiler locks out as a safety precaution. Once the underlying problem has been resolved, a manual reset using the boiler's reset button is required to restore normal operation. Note: Andrews Water Heaters (part of the Baxi Group) primarily serves commercial applications, and fault code definitions can vary between models and production years. If the code behaviour on your unit does not match the description here, always cross-reference with your specific Andrews installation and service manual or contact Andrews technical support directly with your model number to hand.

Causes, fixes & costs for Andrews E42 → · All Andrews codes

Ravenheat E42

E42 on a Ravenheat boiler belongs to the E42–E44 fault group, which Ravenheat's documentation describes as a 'different temperature' error — the control board is comparing readings from its temperature sensors (typically the flow and return NTC thermistors) and finding a difference or pattern that should not be possible if water were circulating properly and both sensors were healthy. Rather than keep firing on readings it cannot reconcile, the board stops the boiler and displays the code. In practice E42 comes down to one of two things: a sensor (or its wiring) drifting out of specification, or a genuine circulation problem — a struggling pump, air in the system or a blockage — making the real temperatures diverge abnormally.

Causes, fixes & costs for Ravenheat E42 → · All Ravenheat codes

Warmflow E42

The E42 code appears on certain Warmflow Agentis combination boiler models and, based on the fault numbering pattern used across the Warmflow range, most likely indicates a domestic hot water (DHW) temperature sensor or thermistor fault. The boiler's PCB has detected an abnormal reading — or no reading at all — from one of the sensors monitoring the hot water circuit, and has shut down or locked out to prevent damage or unsafe operation. It is worth noting that E42 does not appear in all publicly available Warmflow manuals; the code is most relevant to Agentis combi variants. If you cannot find E42 in your model's documentation, contact Warmflow directly on 028 9262 1515 with your exact model number to confirm the definition before attempting any remedial action.

Causes, fixes & costs for Warmflow E42 → · All Warmflow codes

Frequently asked questions

Is the E42 fault code the same on every boiler?

Broadly, yes — on Andrews, Ravenheat and Warmflow the E42 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 E42 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. The underlying repair usually needs a registered engineer. Never open the boiler casing yourself.

Who should I call about a E42 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.