Boilers are cantankerous machines. Everything has to be just right, or these machines will let you know that they are not going to do their jobs properly. If you have an old boiler that is shaking, rattling, or rolling, here is what you should do about each of these movements.
A boiler that shakes has one of two problems. Either it is not securely attached to the floor, or there is too much pressure building up and not enough water inside. Try fixing the first problem, since it is something that is easily fixable. After checking every bolt, hex screw, and nut on the machine, it should be more stable. If it is not, check the water supply line. Sometimes plugs or kinks develop, preventing the boiler from getting enough water. If that does not seem to work, call in an HVAC repair technician and/or a plumber to check the boiler's pressure and internal systems. (DO NOT do this step yourself! It is too dangerous!)
Yikes. A boiler that is rattling has a lot going wrong with it on the inside. Something is loose, or something is definitely broken. Again, never open a boiler yourself to see what is going on. Leave that job up to the boiler repair technician or the plumber. About the best you can do is look all around the exterior of the boiler to make sure there is nothing on top, underneath or behind the boiler that does not belong there and is responsible for the rattling. You would be surprised how often a custodian drops a wrench behind a boiler and then the boiler rattles like crazy.
A rolling boiler is a very dangerous boiler indeed. Whether it is rocking back and forth or appears as though it is going to explode, treat the situation as an emergency one. Shut it down safely, if you can. If you cannot, clear everyone out of the area to prevent injuries. This situation needs to be contained right away, so if you cannot get a plumber or HVAC technician to come right away, keep calling more plumbers and technicians until you can get help.
Also, if necessary, alert other important parties to the fact that you have a boiler with this issue. One such example is alerting the superintendent of schools if the old boiler is located in a school. The children and staff will have to relocate temporarily. Another example is a tenement building. You do not want the boiler to blow and cause more fatalities or injuries.