I have a 1987 Burnham ANS-Z21-13 gas, forced steam boiler that will not shut down when the set temperature has beeen reached, and will run all night. I disconnected the thermostat and the furnace continued to run, so it doesn't seem like the thermostat. It does have 2 pressuretrol controllers (1 was replaced by a tech last year). Could it be a bad pressuretrol controller or a stuck relay somewhere?

It could be either. Look at the setting on the pressurtrol with the higher set point & also at your pressure gauge. Is the boiler pressure higher than the setting?

Yes. Pressuretrol is at 0.5 PSI and the pressure gauge is at 3 PSI. For the past few years that I've owned the house, the Pressuretrol has always been at the lowest setting of 0.5, but the pressure gauge usually sat at about 0 or maybe 1 PSI.