The E13 fault code appears on 6 brands — Andrews, Baxi, Biasi, Potterton, Ravenheat and Remeha — 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.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
E13 brand by brand
The E13 code on an Andrews boiler signals that the differential water flow switch is reading as closed when it should be open. In other words, the boiler's control board is receiving a signal suggesting water is circulating when it may not be — or the switch itself has become stuck in the closed position. This is closely related to the E12 code: where E12 indicates the switch is open when it should be closed, E13 is the opposite condition. Either way, the boiler will typically lock out as a precaution to prevent overheating or damage until the root cause is identified and resolved.
Causes, fixes & costs for Andrews E13 → · All Andrews codes
The E13 code appears on most current Baxi boiler ranges and indicates a differential water flow switch fault where the switch is detected as being stuck in the closed position when the boiler expects it to be open. The flow switch (sometimes called a flow sensor or flow turbine) monitors water movement through the boiler — it detects when hot water taps are opened or the heating circuit is calling for flow. When the boiler's control system finds the switch is not behaving as expected, it locks out to protect the heat exchanger and other components from damage. Important caveat: on a small number of older Baxi models, E13 is instead associated with a heat exchanger thermal fuse having tripped rather than a flow switch fault. Check the label inside your boiler casing or your model's specific manual to confirm which interpretation applies to your appliance.
Causes, fixes & costs for Baxi E13 → · All Baxi codes
The Biasi E13 fault code — also displayed as ER 13 on older Biasi models such as the Riva Plus and Garda, and as E13 on newer models including the Inovia, Rinnova, and Rinnova Adaptive — indicates that the boiler has detected an excessive temperature difference between the flow (flow/mandata) pipe and the return (ritorno) pipe of more than 40 Kelvin (40°C). In practical terms, this means water is leaving the boiler very hot but returning far too cool, which almost always points to a circulation problem within the heating system. The boiler locks out to protect the heat exchanger from overheating. On some Biasi Inovia firmware variants, E13 is described as relating to a faulty pump or primary temperature exceeding 105°C — which is consistent with the same root cause: water is not flowing around the system fast enough.
Causes, fixes & costs for Biasi E13 → · All Biasi codes
The E13 code on a Potterton boiler indicates a flue gas or combustion safety fault. The boiler's control system has detected an abnormality in the combustion or flue gas pathway and has shut itself down as a precaution to protect occupants and the appliance. It is a safety lockout, meaning the boiler will not restart until the underlying problem is resolved. Note that E13 is a distinct code from E133 — E133 specifically relates to ignition lockout or gas supply interruption, while E13 sits earlier in Potterton's fault numbering and relates more broadly to flue gas or combustion safety conditions. E12, the preceding code, concerns a flow/return temperature differential fault. If your display shows E133, that points primarily to ignition or gas supply issues rather than the flue gas safety condition described here.
Causes, fixes & costs for Potterton E13 → · All Potterton codes
The E13 code on a Ravenheat boiler signals a software or firmware fault within the boiler's printed circuit board (PCB). In plain terms, the electronic brain of the boiler has detected an internal error — this could be corrupted memory, a failure in how the PCB communicates with other components, or a configuration problem following a recent board replacement. Until the underlying cause is identified and resolved, the boiler will remain locked out and refuse to fire. Note that Ravenheat is no longer trading as a manufacturer, which means genuine replacement PCBs and other spares are becoming increasingly difficult to source — a factor worth weighing up before committing to an expensive repair.
Causes, fixes & costs for Ravenheat E13 → · All Ravenheat codes
The E13 code appears on Remeha boilers — most commonly the Avanta and Avanta Plus range — when the heat exchanger's built-in thermal fuse has responded to a serious overheat condition. This is the boiler's last line of defence against catastrophic overheating: once the thermal fuse trips, it cannot be reset, meaning the heat exchanger itself is permanently damaged and will need to be replaced. On Avanta Plus combi models, E13 can sometimes relate instead to the domestic hot water (DHW) flow switch or the plate heat exchanger specifically, which may present as a loss of hot water while central heating continues to work. A small number of sources also link E13 on certain model variants to an external sensor or weather compensation fault, so it is worth cross-referencing with your specific model's manual. In any case, E13 is a serious fault requiring a Gas Safe registered engineer — this is not a code you can clear with a simple reset.
Causes, fixes & costs for Remeha E13 → · All Remeha codes
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.
