short story: ancient life-form found in power station

"The Last Salamander", a short story by John T. Phillifent aka John Rackham, first published in New Worlds Science Fiction #132, July 1963, available at the Internet Archive.

From information provided by the OP, this is the third story in John Rackham's series about people with special telepathic/empathic powers called the Extraordinary People or the "X" People; the first two stories in the series were the short story "Dossier" and the novelette "Confession".

Editorial blurb:

In another time and place (as opposed to the world of fiction writing) and under another name, John Rackham works in one of our great power stations. We wonder if the following story has any basis in truth — however remote . . .

Night-shift at the power station:

Cockbum watched, with seeming bland indifference, but he missed none of it. In an hour, almost all of this groaning machinery would be still, the fires would be allowed to dwindle to red masses of glowing coke for a breathing space, until the demand came on again in the morning. Another night-shift, just like thousands that had gone ahead of it into the nothingness of yesterday. A time to read, to chat, to search out odd jobs, to drink tea until it palled. To try to keep awake and attentive, just in case. That was the major problem — how to keep alert and attentive for something which, in the normal course of events, should never happen, just in case it did? The best of machinery, the most ingenious automatics, can fail. That's why you need men, not to work, but to know exactly what to do if something should go wrong.

The blob:

Long before Walter could take a turn with the shield he knew that Cook had spoken the literal truth, although he could not have explained how he knew. This was where that vivid flashback from the past had come from. This was what had thought of a volcano as a pleasant place. He sensed that it was newly born and bewildered, but strong, with a firm grasp on life. Concepts shuttled swiftly in his mind, leaping the gaps in his knowledge. Something Like this could have lived on Earth, eons ago, in the time of great heat; spouting fires from the Earth's bowels and creeping masses of molten lava would have been its proper environment suiting its fantastic chemistry.

But such a life-form must have withered and perished when the fires died down, when the crust settled and became more suited for complex, low-temperature forms, based on carbon-oxygen-water compounds. So long ago that the mind ached at the effort to measure it, things like this had ceased to exist. So how . . .? Then it was his turn with the shield and the tinted glass and he saw a blob without shape, of white-hot slow movement, maybe the size of a football. It nestled among a pile of jagged fragments of ash, on the sloping floor of the hopper and it pulsed. Slowly, as if gasping for breath, it pulsed and wire-veins of orange squirmed across its surface with each heave. Walter was at once reminded of a chicken, newly hatched and a wet, bedraggled mess, struggling for breath, gaining strength. That must be it. This thing had been an egg, or a spore, waiting all these unthinkable ages for the right conditions to trigger off its burst into life. Looking at it, he felt a greater, powerful sense of identity with it, knew that it was momentarily exhausted, hungry, but had reached a self-sufficient stage. It didn't need outside heat any longer. Given the right food, it could, and would, generate its own and grow.

It's dead:

There came a sudden blue-white glare, blinding in its intensity and the hissing spit-crack thunder of discharge, the choking stink of ozone and a sudden darkness and stillness. His head ringing, eyes stunned into blood-red glare, Walter heard the dismal, heart-stopping wail of dying machinery and far-off shouting. Ahead of him there was a dull red mound of dying fire, dwindling to a skeleton mass of running, winking sparks, struggling to make networks — and then nothing. He knew it was dead, because he had 'heard' its death-scream and felt it. That feeling of treason, of betrayal, came back stronger than ever. Its only crime had been to be born several million years too late and alone. And he had killed it.