E31 Boiler Fault Code: What It Means on Every Brand

The E31 fault code appears on 5 brands — Alpha, Andrews, Keston, Ravenheat and Warmflow — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Lockout — engineer likely 5 brands use this code Meaning differs by brand

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 E31 means	Severity	DIY?
AAlpha	The E31 code on an Alpha boiler points to a problem with the heating flow NTC thermistor — the sensor that monitors the temperature of water leaving the heat exchanger on the central… Full guide →	Lockout — engineer likely	No
AAndrews	The E31 code on Andrews boilers and water heaters (including ECOflo and MAXXflo series) indicates that the control board has detected a problem with the heating circuit flow sensor or flow… Full guide →	Engineer may be needed	No
KKeston	The E31 code signals a problem with the flow temperature sensing circuit — the part of the boiler that monitors how hot the water is as it leaves the heat exchanger. Full guide →	Lockout — engineer likely	No
RRavenheat	The E31 code on a Ravenheat boiler signals that the OpenTherm communication link between the boiler and its connected thermostat or controller has broken down. Full guide →	Lockout — engineer likely	Some checks
WWarmflow	The E31 code appears on Warmflow Agentis Series boilers when the main control board can no longer communicate properly with the remote control unit. Full guide →	Engineer may be needed	No

E31 brand by brand

Alpha E31

The E31 code on an Alpha boiler points to a problem with the heating flow NTC thermistor — the sensor that monitors the temperature of water leaving the heat exchanger on the central heating circuit. When this sensor reports a reading that falls outside the expected range, or sends no signal at all, the boiler locks out and displays E31 to protect the system from running with unreliable temperature data. The boiler can be reset manually once the underlying cause has been resolved. Note: Alpha fault codes vary between model ranges, and E31 is not universally documented across every Alpha product. If your boiler displays a slightly different code pattern, cross-reference your model's manual or speak to a Gas Safe engineer with your exact model number to hand.

Causes, fixes & costs for Alpha E31 → · All Alpha codes

Andrews E31

The E31 code on Andrews boilers and water heaters (including ECOflo and MAXXflo series) indicates that the control board has detected a problem with the heating circuit flow sensor or flow switch. In plain terms, the boiler's electronics are unable to get a reliable reading of how much water is circulating through the system. This could be because the sensor itself has failed, because of a wiring fault between the sensor and the PCB, or because water is not flowing adequately for the sensor to register correctly. The fault is manually resettable once the underlying cause has cleared, but if it keeps returning the boiler should not continue to be operated — persistent faults can cause damage to internal controls. Note: Andrews fault codes can vary between product ranges and control board generations, so always cross-reference with your specific model's documentation or contact Andrews Water Heaters directly if you are unsure.

Causes, fixes & costs for Andrews E31 → · All Andrews codes

Keston E31

The E31 code signals a problem with the flow temperature sensing circuit — the part of the boiler that monitors how hot the water is as it leaves the heat exchanger. Importantly, what E31 means depends on your specific Keston model: on the C36 Combi, it indicates an open circuit in the flow sensor (an interrupted electrical signal), while on the C40 and C55 Combis, it indicates a short circuit in the flow thermistor (an unwanted electrical connection, often caused by moisture). In both cases the boiler detects that it can no longer trust its temperature readings, locks out as a safety precaution, and will not restart until the Reset button is pressed. Left unresolved, you will have no heating or hot water.

Causes, fixes & costs for Keston E31 → · All Keston codes

Ravenheat E31

The E31 code on a Ravenheat boiler signals that the OpenTherm communication link between the boiler and its connected thermostat or controller has broken down. OpenTherm is a digital, two-way protocol that allows a compatible thermostat to continuously adjust the boiler's heat output in real time — rather than simply switching it on and off. When E31 appears, this dialogue has been interrupted, and the boiler cannot receive the commands it needs to operate correctly. The fault may be triggered by something as minor as flat thermostat batteries or a temporary signal dropout, but it can also point to wiring issues, a faulty thermostat receiver, or a problem with the boiler's PCB.

Causes, fixes & costs for Ravenheat E31 → · All Ravenheat codes

Warmflow E31

The E31 code appears on Warmflow Agentis Series boilers when the main control board can no longer communicate properly with the remote control unit. In plain terms, the data link between the boiler and its remote has broken down — either in the wiring, at a connector, or within the remote unit itself. The code may display in blue (warning) or red (serious error) on the LCD. Two closely related codes to be aware of are E32 (an MMI/control PCB error originating at the remote control end) and E62 (an MMI/control PCB error on the boiler itself); an engineer investigating E31 will often check for these as well.

Causes, fixes & costs for Warmflow E31 → · All Warmflow codes

Frequently asked questions

Is the E31 fault code the same on every boiler?

No. E31 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a E31 fault myself?

On some brands there are safe homeowner checks first — typically system pressure, the condensate pipe in cold weather, and a single reset. Where the code is a simple pressure or reset condition, that may be all it needs. Never open the boiler casing yourself.

Who should I call about a E31 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.