Mechanical Engineer (Contractor)

Design, build and commission hydraulic test rigs and prototype products that integrate with heat pumps (buffer tanks, hot water cylinders, heat exchangers, circulation and modulation hardware, and similar).

Carry out hands-on assembly and plumbing of water-side and refrigerant-adjacent systems - pipework, fittings, pumps, valves, sensors and controls.

Instrument rigs with temperature, flow and pressure measurement, and run structured test campaigns to characterise both systems and components performance.

Diagnose and troubleshoot hydraulic, thermal and mechanical issues on live systems, and feed findings back into the design.

Work closely with the wider R&D team to iterate designs quickly, balancing performance, cost, manufacturability and serviceability.

Produce clear documentation: test plans, build instructions, results write-ups and design records.

Degree in Mechanical Engineering (or a closely related discipline).

Minimum 5 years' relevant experience in an R&D, product development or test environment.

Demonstrable heat pump knowledge - you understand how heat pumps work, their operating envelopes, and how the hydraulic system around them behaves (flow, temperature, ΔT, defrost, modulation, etc.).

Strong hands-on experience - this is the most important requirement. You can build, plumb, commission and fault-find systems yourself, not just specify them. Practical plumbing and pipework skills are essential.

Experience working with hydraulic systems - pumps, valves, heat exchangers, tanks, pipework and the behaviour of water-side circuits.

Comfortable instrumenting rigs and interpreting test data to draw engineering conclusions.

CAD proficiency for designing rig components and prototype parts.

Able to work independently and using own initiative on-site in Slough and move quickly in a fast-paced R&D environment.

Experience developing products specifically intended to operate with heat pumps (buffer tanks, hot water cylinders, DHW modules, hydraulic interface units, etc.).

Familiarity with refrigerant-side systems and relevant safety considerations.

Thermal/fluids analysis skills (thermodynamic modelling, or sizing calculations) to support design decisions.

Experience in setting up, running, and interpreting FEA (structural/thermal) and CFD analyses on complex systems. 

Relevant trade or industry qualifications (e.g. plumbing, F-Gas, G3 unvented hot water) - not required but valued.

Experience taking products through prototype into early manufacture.

A genuinely hands-on R&D role at the leading edge of UK heat pump accessory product development.

A well-equipped facility and the freedom to build and test real hardware.

A collaborative team that moves fast and values practical engineering judgement.

Competitive contract day rate, commensurate with experience.

Octopus Energy is a unique culture. An organisation where people learn, decide, and build quicker. Where people work with autonomy, alongside a wide range of amazing co-owners, on projects that break new ground. We want your hard work to be rewarded with perks you actually care about!