Mechanical Engineer (Contractor)

Octopus Energy's R&D team in Slough is developing the next generation of heat pump systems and hydraulic products that surround them. We're looking for a hands-on R&D Engineer to join the team on a contract basis to help design, build, test and iterate hardware that works alongside heat pumps. This is a practical, workshop-floor role as much as a design one. You won't just specify components - you'll be plumbing rigs, commissioning systems, instrumenting test loops and getting real data out of real hardware. We need someone who is equally comfortable with a CAD model, a P&ID and a pipe wrench. If you like the idea of taking a concept from a sketch to a working prototype on a test rig within weeks, this is the role. What you'll do 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. Essential requirements 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. Desirable 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. Why else you'll love it here! 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! Visit our perks hub - Octopus Employee Benefits If this sounds like you then we'd love to hear from you. Are you ready for a career with us? We want to ensure you have all the tools and environment you need to unleash your potential. Need any specific accommodations? Whether you require specific accommodations or have a unique preference, let us know, and we'll do what we can to customise your interview process for comfort and maximum magic! Studies have shown that some groups of people, like women, are less likely to apply to a role unless they meet 100% of the job requirements. Whoever you are, if you like one of our jobs, we encourage you to apply as you might just be the candidate we hire. Across Octopus, we're looking for genuinely decent people who are honest and empathetic. Our people are our strongest asset and the unique skills and perspectives people bring to the team are the driving force of our success. As an equal opportunity employer, we do not discriminate on the basis of any protected attribute. Our commitment is to provide equal opportunities, an inclusive work environment, and fairness for everyone.