pressuretrol is a high limit only
A pressuretrol should be set up as a high limit device only, except in some large instututional settings where steam pressure is maintained at all times. Normally, the call for heat starts the boiler by closing a set of contacts in the thermostat. The pressuretrol is wired in series with the thermostat and the other safety cutout devises, so the only time it has any effect is if the boiler has run long enough that pressure has built up to the cut out setting. At that point, the pressuretrol contacts open, and the boiler stops firing until the pressure drops. A faulty pressuretrol should not cause the boiler to fire continuously, if it is wired properly.
It sounds to me like their may be another reason for the problem. Does this boiler supply domestic hot water? If so, there is another device. Usually it is a well mounted thermostat on the boiler that maintains the boiler temperature at a given set point, usually around 180 F. If this is set too high, or if it has failed, or if the conductive grease in the well has dried up, etc., it may be letting the boiler get hot enough to steam before it shuts the boiler down.
Hope this helps and that you solve the problem. I would like to know how this turns out.
Dave in Quad Cities, America
Pennco 40M-1050SA Cast Iron Atmospheric Boiler. Input 1,050,000. Downfired to 600,000 BTU Lo-fire, 825,000 BTU Hi-fire input,
System = Early Dunham 2-pipe Vapor/Vacuum (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2
Current connected load EDR= 1,287 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 8 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
Projects -
http://home.mchsi.com/~david.cordes/index.html and
http://home.mchsi.com/~bpattsch/index.htmlThis post was edited by an admin on August 23, 2010 10:35 AM.
