The growth in the number of disputes with governing bodies is causing alarm, with the union reporting an increase in the number of heads who are under suspension.
David Hart, general secretary of NAHT, said heads were being suspended because they did not see eye-to-eye with their governing bodies and because inspections were creating a "football-manager syndrome", where the head has to carry the can for poor reports and low league-table placings.
Ian Bruce, vice chair of the union's south-west confederation, said it would be foolish to attribute bad relations solely to governors, but in some cases they were stepping over the mark: "We do not find it acceptable for a head to return to the office to find governors who have gone through files and then who make comments about the headteacher's efficiency."
He said that governors should leave the day-to-day running of schools to the head, but those who are happy to take the lead from the head when things were going well should not then disassociate themselves when things go wrong.
David Grey, the south-west region's branch secretary, said that governors, parents and teachers should be allies. But heads as professionals should be at the helm. It was the Government, he said, which wanted more lay people involved in schools. Therefore the Government should ensure they are trained.
Delegates complained that some governors liked the power, but walked away from responsibility, others were ignorant of the teachers' pay and conditions document.
The union's recently published draft code of practice says governors should always make an appointment before they visit schools and should see the head before they leave. Heads should be able to attend all governing body meetings, provided they are not the subject of disciplinary action.
Walter Ulrich, spokesman for the National Association of Governors and Managers, opposed a code of conduct. He said only a few governors were trying to do things sensibly left to heads. "Governors are not just heads' supporters clubs. In many cases they do not do all their tasks and the head moves into the vacuum. But where they do take on their full role, they find the head does not like it," he said.