Steam Heating Systems:
Testing a steam heating system is very similar to checking a hot water heating system. I'll mention some differences, but it may seem repetitive to the hot water system section. A steam system has a sight glass on the side of the boiler. This allows you to see the water level in the boiler. The sight glass should be 1/2 to 3/4 of the way full. It shouldn't be completely empty or completely full which can cause problems. The sight glass level allows you to see that there's air and water in the boiler. This is because you're making steam and you've got to have room for the heated water to boil and create steam.
A steam system has a sight glass on the side of the boiler. This allows you to see the water level in the boiler. The sight glass should be 1/2 to 3/4 of the way full.
If the sight glass is completely filled with water, it could mean that the pipes are flooded because the water supply valve for the boiler was left open. This will lead to water discharging from the vents on the radiators. If the sight glass is completely empty, it could mean that the boiler has no water in it. This is a dangerous condition if the burner turns on because there won't be anything to transfer the heat to. For safety, there should be a low water cutoff switch on the boiler in case the water level drops too low. These devices will automatically turn off the boiler when the water level gets too low for proper operation of the heating system. An automatic water feed can be installed on steam heating systems. These devices are attached to the water supply pipe leading into the boiler. They automatically monitor the water level inside the boiler and add water whenever necessary.
Steam heating systems have supply and return plumbing lines to carry steam and condensation. You have supply lines that bring the steam to the radiators in each room. The return lines bring the condensation water back to the boiler after the steam has given off its heat. After the steam gives off its heat, it condenses into water and is reboiled and recirculated. There should be at least one radiator in each room.
There are no circulator pumps like on a hot water system, because steam rises on its own. As a result, steam systems have wider diameter pipes than forced hot water systems. Separate heating zones are established by zone valves on the supply pipes to open and close the circulation of steam.
Check all heating pipe joints for rust or leaking conditions that'll require repairs. You'll usually find some rust unless it's a new unit. Open any panels on the heating system that don't require tools. You should be able to view the heat exchanger and the firebox. Check the heat exchanger for rust or leaking conditions. Check the condition of the firebox where the burner flame is.
There's no water pressure reducing valve, backflow preventer or expansion tank for steam systems. This is because there's only water in 3/4 of the boiler and these items aren't needed. The supply and return lines have mostly air in them to allow for the passage of the steam.
Check for a properly operating pressure gauge. The gauge should move while the boiler is being tested. The proper operating pressure for a steam heating system is 2-5 psi. Make sure the pressure doesn't go too high and record the readings you get. There may be a water temperature gauge combined with the pressure gauge also. Monitor the water temperature during the test and record the readings.
Steam heating systems should have an upper limit switch installed directly on the boiler. The upper limit switch looks like a small electrical relay box. It's attached to the boiler by a copper pipe that's looped in the shape of a pig tail. The purpose of the pig tail is to trap water in the loop so the steam in the system doesn't rust out the upper limit switch controls. If the pressure in a steam heating system gets too high, then the upper limit switch is designed to electrically turn off the burner so that the system pressure doesn't keep rising.
The pressure relief valve must be located directly on the boiler unit for proper operation. It must be piped to within eight inches of the floor to prevent scalding anyone when the valve discharges.
Check for a pressure relief valve on the boiler. This is a safety device that helps prevent the heating system from becoming dangerously high in pressure. If the pressure reaches 15 psi, then the valve will discharge to relieve the system so the boiler won't explode. When water or steam discharges from this valve, it indicates a problem condition. When this happens, the system must be checked out immediately by a licensed heating contractor. Pressure relief valves should not be rusty and they must be located directly on the boiler for proper operation. The valve must be piped to within eight inches of the floor to prevent scalding anyone if it discharges.
There should be a drain valve on the lower part of the boiler. Drain a small amount of water into a bucket to determine the color. You can get an indication of whether the system has been maintained and properly drained monthly by the color of the water.