E10 varies wildly by brand, and two brands use it for opposite-sounding faults: on Alpha it is low system pressure (a filling-loop top-up), while on Baxi and Potterton it is an outdoor temperature sensor fault that has nothing to do with pressure. Biasi uses E10 for a lockout, Keston for an internal board error, Remeha for a circulation problem, and Ravenheat for a pressure problem in either direction. Match your brand in the table before you touch the filling loop.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
E10 brand by brand
The E10 fault code on Alpha boilers is triggered when the boiler detects that system water pressure has dropped below the safe operating threshold — typically under 0.6 bar. As a safety measure, the boiler locks out and will not fire until the pressure is restored and the fault is cleared. On the vast majority of current Alpha models (including the E-Tec, Evoke, Intec, and CD18R ranges), E10 relates to low pressure. However, at least one source notes that on certain older Alpha models E10 may instead indicate an overheat condition — so if repressurising does not clear the fault, always check your specific model's manual or contact Alpha support directly.
Causes, fixes & costs for Alpha E10 → · All Alpha codes
The E10 fault code on a Baxi boiler points to a problem with the outdoor (external) temperature sensor. This sensor feeds real-time outside temperature data to the boiler's PCB so it can fine-tune its output — a feature known as weather compensation. When the boiler detects that the sensor is disconnected, reading outside its expected range, or returning implausible values, it logs E10 and may lock out to protect performance. On most modern Baxi models (Duo-tec, Platinum, and combi ranges) this is the accepted meaning. On a small number of older or variant models, E10 has been associated with a central heating NTC or low water pressure condition — if you are unsure which applies to your boiler, check the model-specific manual or ask a Gas Safe engineer.
Causes, fixes & costs for Baxi E10 → · All Baxi codes
The E10 (also displayed as ER 10) fault code means your Biasi boiler has shut itself down — locked out — because the flue gas probe or thermal fuse has intervened. These components sit within the flue circuit and monitor flue gas temperatures during combustion. When either one detects conditions outside safe operating limits, the boiler cuts out immediately as a precaution. This is a safety lockout, not a nuisance trip, so the boiler will not restart on its own until the underlying cause is identified and resolved. A single reset may clear it temporarily, but if the code returns, there is a genuine fault that needs a Gas Safe registered engineer to investigate.
Causes, fixes & costs for Biasi E10 → · All Biasi codes
The E10 code on a Keston boiler signals that the control board (PCB) has detected an internal error and cannot operate normally. When this code appears, the boiler enters a lockout state and shuts down completely — it will not restart on its own. You must press the boiler's dedicated reset button to attempt a restart once the underlying issue has been addressed; simply switching the power off and back on will not clear the lockout.
Causes, fixes & costs for Keston E10 → · All Keston codes
The E10 code on a Potterton boiler indicates a problem with the outdoor temperature sensor. This sensor — fitted to an external wall and wired back to the boiler — feeds real-time outside air temperature data to the boiler's controls, allowing it to modulate its heat output based on weather conditions (a process called weather compensation). When the boiler cannot get a valid reading from this sensor, it logs E10 and may restrict or stop normal operation. Note: E10 is a completely separate fault from E110, which relates to boiler overheat — the two are sometimes confused but have nothing in common.
Causes, fixes & costs for Potterton E10 → · All Potterton codes
The Ravenheat E10 fault code signals a water pressure problem — but the exact direction of that fault (too high or too low) can vary depending on which Ravenheat model range you own. On CS and CSI series boilers, most sources point to E10 indicating excessively high system pressure. On some WH and other variants, heating engineers report it appearing when pressure has dropped too low. In either case, your boiler has detected that pressure has moved outside the safe operating band — typically 1.0 to 1.5 bar at rest — and has locked out to protect itself. The first thing to do is glance at the pressure gauge: if the needle is above 2.5 bar you have a high-pressure fault; if it is below 0.8 bar you have a low-pressure fault. If you cannot locate your specific model's manual, this distinction will tell you which direction to focus on. Both scenarios are covered on this page.
Causes, fixes & costs for Ravenheat E10 → · All Ravenheat codes
The E10 code appears on Remeha boilers when the appliance detects that water is not moving through the system during its automatic venting or start-up sequence. In plain terms, the boiler is trying to push water around the circuit but is not sensing any meaningful flow. As a safety response, the boiler locks out and stops producing central heating or hot water until the underlying cause is identified and the fault is cleared.
Causes, fixes & costs for Remeha E10 → · 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.
