Hitachi
The Hitachi low current trip function for L300P and SJ300 inverters protects pumps by triggering an E12 fault code when undercurrent conditions, like dry running, are detected.
The Hitachi low current trip function for pumping applications is a specialized monitoring feature found in L300P and SJ300 series inverters. Introduced in 2004, this function protects pumping systems by detecting undercurrent conditions, such as fluid absence or motor no-load states. This technical reference covers the operation of the E12 external trip signal and its integration within domestic and commercial heating or fluid management systems using Hitachi inverter technology for precise motor control.
Stick a QR tag on the case, scan it on every service and give your customer a permanent, shareable service history they can pull up from any phone.
Permanent, shareable service history
One QR scan on the boiler surfaces every previous fault, part change and visit — no paperwork to dig out.
Free AI fault diagnostics, built in
Every tag you fit unlocks the AI diagnostic tool for that exact model — paste a fault code, get a ranked cause list.
Your name on the boiler forever
When the next service or breakdown comes around the homeowner scans and sees your number first.
First 12 BoilerTags are free
Tag every install and service you do from now on — the subscription only kicks in once you scale past your first dozen.
Diagnosing a fault on a Hitachi L300P right now?
Try the free AI fault diagnostics tool — no signup needed.
Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
The Hitachi low current trip function for pumping applications is a legacy technical implementation designed for the L300P and SJ300 inverter series. According to manufacturer documentation from 2004, this function serves as a critical protection mechanism for pump motors by monitoring for undercurrent conditions. In typical pumping applications, a significant drop in current often indicates a dry run scenario where fluid is absent or the motor is operating without a load.
The primary diagnostic indicator for this function is the E12 fault code. Per the technical datasheet, the E12 code represents an External Trip. While this can be triggered by an external signal via the [EXT] terminal, in the context of this specific pumping function, it is used to shut down the inverter when the current falls below a predefined threshold. This prevents mechanical damage to pump seals and bearings that would otherwise occur during dry operation.
The L300P and SJ300 inverters are identified as the primary hardware variants supporting this specific logic. These units are high-performance inverters capable of managing complex motor loads. The low current trip function is particularly relevant for engineers maintaining older heat pump installations or fluid circulation systems where these Hitachi inverters provide the variable speed drive. The documentation classifies this as a product manual supplement rather than a full heat pump specification, focusing strictly on the inverter response to load loss.
Engineers should note that the E12 trip is a lockout condition intended to protect the hardware. When troubleshooting, the presence of an E12 code requires a verification of the fluid levels and the integrity of the hydraulic circuit before resetting the inverter. While modern Hitachi heat pumps integrate these protections into the main control logic, the L300P/SJ300 series remains in service across many UK industrial and domestic HVAC interfaces. Understanding the specific parameters of the low current trip ensures that system downtime is minimized and that the root cause of an undercurrent event—typically a hydraulic failure—is addressed rather than simply clearing the electronic fault.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/heat-pumps/hitachi/l300p#fault-e12 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| E12 | External Trip Show causes & actionsThe inverter will trip when the External Trip [EXT] signal is turned on from outside the inverter. Likely causes
| Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Triggered by fault code E12.
Common questions from engineers and homeowners about the Hitachi L300P.
We hold the Hitachi L300P manual — and every other UK boiler and heat pump brochure. Sign up and pull any model up from your phone, on the job.
Sign up to access brochuresTag it before you leave. Next scan shows every service, fault and part change — and the AI diagnostic tool is free on every tag you fit.
Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 30 April 2026.