Never mind Agas and Rayburns, it's the Pither Stove, unaltered in 70 years, that the cognoscenti want. Jack O'Sullivan meets Pither fanatics and their patron saint
To the uninitiated it looks like a tall office ashtray. "A pot for cooking spaghetti," says one owner. "One of those large coffee servers you find in canteens," suggests another. The Pither Stove is unpretentious. Yet, to devotees, it is the hearth and soul of their homes. An unobtrusive, stylish companion with a simple, cylindrical stainless-steel casing, it stands year after year in a corner of a room, and pours out enough warmth to raise the dead.

Internally, its workings are just as simple. A compartment at the top filled with anthracite beans gravity-feeds the fire, throwing heat out over a huge area and leaving the finest of ash in a tray that needs to be emptied just once a day. It is as easy to control, via the air vent, as some of the most sophisticated heating systems.

You will find Pither devotees all over the country, members of an unofficial fan club - instead of flashing their lights at each other like VW Beetle drivers, they talk of how long their Pither will burn without needing a fuel top-up. Pithers are smouldering in barn conversions, churches, even canal barges. "It's my friend," says Mary Fedden, painter and member of the Royal Academy. For 40 years, hers has heated the large studio room where she lives, eats and sleeps. "It glows at night and throws wonderful light on to the ceiling. Everybody likes sitting around it. It's very handy for keeping dishes warm in case people want a second helping. And it's lovely to sleep with a Pither, because it will burn right through the night."

Brian Clemens, creator of The Avengers and The Professionals, shares Mary Fedden's passion. "It's a wonderful piece of machinery. You could leave it for a whole weekend, come back and it would seem like a dead fire. Then you pulled out the damper and within 10 minutes you had a great fire again." But, like other enthusiasts, Clemens was forced to abandon his first love for second-best, a wood-burning stove, because he couldn't find vital spare parts. "I greatly regret having to get rid of it," he says.

And there were those who completely lost the faith. Nonie Niesewand, the Independent's architecture and design correspondent, used to own a Pither. "There was no stopping my children sitting in the coal bucket and then on the sofa. I ended up calling out the fire brigade, because hot coals spat out and the wooden floors started to burn. I decided then it was unsafe. It was a design statement but I grew out of it."

The late Ruskin Spear, portrait painter and Royal Academician, stopped using his because it burned so fast it became clogged up. His wife, instead, keeps a red light in it.

In short, the Pither might have faced a slow extinction had it not been for one man. Bill Tierney, "Mr Pither Stove", has kept the flame alive through the hard days since the Seventies when no architect's or artist's home was complete without this shiny hot icon quietly warming the chilly minimalism. In the wilderness years, Mr Tierney, an engineer from Staines, Middlesex, toured the country alone, sweeping flues and keeping at least some of the fires burning.

Meanwhile, the rights to the design passed through several companies, none of which bothered much with this design gem. One pair of owners even sacrilegiously altered its name, briefly, to Wade and Lewis, after their wives, says Mr Tierney. But in the past few years Pither prospects have been hotting up. Mr Tierney, 58, finally bought the rights for just pounds 3,000 four years ago, after a quarter of a century on the job. "It was a gift to get it," he says. Since then, he has begun building Pithers again using original castings and mouldings. It's more rewarding, he says, to engineeer a whole product than to make parts, as he did before, for racing cars. Thanks to Tierney, fans now know there is no shortage of new side cheeks, fire bars, nozzles, tip trays and damper blades. No sooner had this news reached Brian Clemens than he was hot on the trail of a new burner for his home.

The Pither is fashionable once more. It went out of favour when gas central heating came in and fiddling around with coal buckets was considered too messy. But the steel frame has been spotted again, lurking in the background, in recent editions of Homes and Gardens, Country Living and Elle Decoration. Tierney is making a dozen a month, and has had an request from Adelaide for 300 burners. The price is also rising. A stainless-steel model, which would have cost you pounds 275 in the Eighties, now sells for pounds 675.

There are many stories about where the Pither originated. Some say that the internal workings were designed for stoves left burning for days in Norwegian huts, to provide refuge for lost skiers. Others reckon it came from France in the 19th century. There are several different models - with black, brass and copper casing, known by such names as the Gothic, the Sheraton and the Victorian - which are almost impossible to find today. But the icon is the stainless-steel "studio" model, created in the Twenties.

How does Bill Tierney explain his burner's restored popularity? "People," he says, "have had enough of Victoriana, of decorating with heavy furniture. All they want now is simplicity." And many of the features that made the Pither attractive in the Seventies still apply. Its reliance on anthracite makes it less polluting than wood burning, which is banned in many cities, and tars up flues. It is efficient, producing little waste. It remains stylish, freestanding, so it liberates you from the traditional living- room culture of two sofas around the fire place. And it's cheap to run - the average burner uses about pounds 250 worth of fuel every half-year, and can heat a whole house, including water. Tierney is currently building a conservatory and Jacuzzi in his back garden for his wife, Maureen, who has multiple sclerosis. The centrepiece will inevitably be one of his old friends.

The greatest enthusiasts are probably the Barnes family of Norfolk, who qualify as chief Pither clan. George Barnes, an architect, confesses to "a longstanding affair" with Pithers. "The fundamental principle," he says, "is to light up in September. Then you don't let them go out until Easter."

Barnes (or more usually his wife) has been feeding his Pither with anthracite beans for 30 years. He also designs his favourite burner into modern houses. He bought two of his daughters Pithers when they settled down. His son, Oliver, a boat builder who recently married, was the latest of the younger generation to have the inevitable wedding present installed.

"They look nice," says Oliver Barnes. "They are easy and clean to run. They give off a very good heat, not a stuffy heat like a radiator. They never go out and they require the minimum of maintenance. There are 22 people at my parents' home for Christmas, when we all sit around in front of the Pither."

Among the aficionados, there is a quiet camaraderie. Richard Russell, a London-based architect, says that a complete stranger saw his burner through a window and, having one herself, felt compelled to knock on the front door and make contact. "It's like dogs meeting," says Mr Russell of fellow owners. "There is a common smell. You have a starting point." Such was the appeal of his first Pither that, when he was selling his former home, the buyer threatened to withdraw from the sale if the Pither wasn't left behind. "Fortunately, Bill fixed me up with a replacement," he recalls.

"I like to keep an eye out for the 6,000 people I have dealt with over the years," says Mr Pither Stove. "Some of them, I suppose I have passed on now. But I'm sure of one thing: none has died of hypothermia"

Bill Tierney can be contacted at 7 Berkley Close, Moor Lane, Staines, Middlesex (01784 457896)