5 km Deep and Back Again: United Downs Overcomes Pump Failure to Put UK’s First Geothermal Power Plant Within Weeks of First Electrons

United Downs: Britain’s First Deep Geothermal Power Plant Edges Closer to the Finish Line After High-Stakes Pump Swap at 5.2 km

Cornwall, UK – November 2025

By: Robert Buluma

Five kilometres beneath the rolling hills of Cornwall, in one of the deepest onshore wells ever drilled on British soil, a quiet but pivotal drama has just played out. After months of frustration, the failed downhole pump that threatened to derail the United Downs deep geothermal project – the UK’s first attempt to generate electricity from hot granite – has been pulled to surface. In its place, a new high-temperature Electrical Submersible Pump (ESP) supplied by SLB (formerly Schlumberger) is being readied for deployment 1,400 metres below the rig floor, inside a 5,275-metre production well that still holds the record as the deepest onshore borehole in the United Kingdom.

The man at the centre of the operation, Ryan Law, Founder and CEO of Geothermal Engineering Ltd (GEL), has been unusually candid on LinkedIn about the setback and the recovery. His posts, complete with moody photographs of cranes silhouetted against Cornish skies, have become must-read updates for the European geothermal community.

“Over the past four months we’ve been running through the commissioning process for the first geothermal #electricity plant in the UK at our United Downs site in Cornwall,” Law wrote in October. “Unfortunately, the deep Electrical Submersible Pump from Baker Hughes stopped working and is being replaced… This has obviously been very frustrating.”

Three weeks later, the tone had changed to cautious optimism: “the non-functioning Baker Hughes unit has now been removed and the new SLB unit is ready to install – a mere 1,400 metres below the ground in our 5,200 metre geothermal well. So, here is a picture of some nice new tubing from Marubeni Corporation. A big thanks to them for delivering so quickly.”

Those two posts, accompanied by striking images of gleaming new Japanese tubing laid out like silver rails and a red crane hoisting equipment against a bruised sky, tell a bigger story than mere project logistics. They mark the moment when Britain’s decades-long wait for home-grown geothermal electricity finally moved from “if” to “when”.

 The Project in Context

United Downs is not just another renewable energy scheme; it is the flagship demonstrator for an entire new industry in the UK. Drilled between 2018 and 2021 at a cost of more than £40 million, the site comprises two deviated wells:

 Production well UD-1: 5,275 m measured depth (4,567 m TVD), bottom-hole temperature ~195 °C

Injection well UD-2: 2,393 m measured depth

Hot brine is produced from naturally fractured Carnmenellis granite, sent to Exergy’s 3 MWe Organic Rankine Cycle (ORC) binary power plant, and then re-injected – a closed-loop enhanced geothermal system (EGS) in a region with no active volcanism.

When fully operational, the plant will deliver:

Up to 3 MWe of continuous, weather-independent renewable electricity (enough for ~7,500 homes)

- At least 10 MWth of direct heat for industrial users and the planned Eden Deep geothermal heating network

A template for replicating the model across Cornwall’s five major granite batholiths, which together represent an estimated 5–10 GW of dispatchable low-carbon power – more than the UK’s remaining nuclear fleet.

The project has been funded by a mixture of public and private money: £10.6 million from Cornwall Council, £5 million from the European Regional Development Fund, £18 million of private equity, and a £17.6 million grant from the UK Government’s Getting Building Fund. It is the centrepiece of Cornwall’s ambitious Geothermal Local Development Strategy.

The Pump That Nearly Broke the Dream

Downhole pumps are the unsung workhorses – and frequent heartbreakers – of deep geothermal projects worldwide. At United Downs, the fluid must be lifted from more than 4 km depth, through brine that is 175–195 °C, heavily saline, and laden with dissolved gases. Only a handful of manufacturers can supply equipment rated for such conditions.

The original pump was a high-temperature REDA ESP from oilfield giant Baker Hughes. It was run in hole in early 2025 and initially performed well during short flow tests. However, during extended commissioning this summer, the unit failed catastrophically, forcing the team to execute one of the most complex workovers ever attempted on a British onshore well: pulling 5.2 km of production tubing, recovering the dead pump, and running a new string.

“Retrieving a failed ESP from that depth is not trivial,” one industry insider commented. “You’re talking weeks of rig time, millions in cost, and the ever-present risk of getting stuck.”

The replacement pump from SLB incorporates lessons learned from similar ultra-hot geothermal and oilfield applications (notably the 200+ °C wells in Iceland and Indonesia). It features advanced motor insulation, redesigned protectors, and materials qualified for prolonged exposure to aggressive Cornish brine.

Supply Chain Resilience

Perhaps the most encouraging aspect of the recovery has been the speed with which specialist equipment was mobilised. High-grade chromium tubing capable of surviving years in hot, corrosive conditions was delivered in weeks by Marubeni Corporation of Japan – a testament to the growing maturity of the global geothermal supply chain.

Meanwhile, the surface plant – Exergy’s air-cooled ORC turbine – has continued to perform flawlessly during commissioning with temporary surface pumps, giving the team confidence that, once the new downhole pump is running, first power will follow rapidly.

 What Success Would Mean

If United Downs generates its first geothermal electrons in early 2026 as now expected, it will end a 50-year wait. Britain first drilled for geothermal heat in the 1970s “Hot Dry Rock” programme at Rosemanowes, just a few miles from United Downs. That project proved the science but was abandoned in the 1990s amid low oil prices and lack of political support.

Three decades later, the context could not be more different. Net-zero mandates, record energy prices, and energy security concerns have put geothermal firmly back on the agenda. Cornwall alone has planning consent or applications in place for more than a dozen deep geothermal projects. Success at United Downs would de-risk the entire pipeline.

As Ryan Law wrote in his October post: “Hopefully the new ESP from SLB will finally enable us to start producing electricity early next year.”

Those words, written beside a photograph of a crane lifting equipment under a brooding sky, carry the weight of an industry on the cusp of breakthrough.

GEL To Operate First UK Geothermal Power Plant at Cornwal

The pump is ready. The tubing is on the rig floor. Five kilometres down, hot water is waiting.

Britain’s first deep geothermal power station is no longer a question of if, but of when the switch is thrown.

Source: Ryan Law on LinkedIn, 2

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