Mansell Wallace has stepped down as Chelmsford City chairman after five years at the Conference South side.
The Clarets have reached the play-offs in four of the five years since the 64-year-old took over.
"I've had two heart attacks, a stroke and a quadruple by-pass. I'm not the person to be driving the club on for the next 10 years," he told BBC Essex.
In a statement, the club said it was surprised by the decision and will hold an emergency board meeting next week.
Meanwhile, boss Mark Hawkes has appointed former Southend United midfielder Kevin Maher as head coach.