Flooding in Steam Boilers

Flooding Defined

• A steam boiler is said to be flooded when the water level in the boiler is too high for normal generation of steam. When a flooded boiler sends water into the heat distribution system rather than pure steam, the system clatters and bangs, and radiators toward the ends of the steam lines get no heat. When everything in the system is working correctly, the volume of water returning to the boiler is almost equal to the volume of water that leaves the boiler in the form of steam. Some steam always escapes from the heating system rather than condensing and returning to the boiler. An automatic water feeder makes up any shortfall in the volume of returned water.

Flooding Causes

• In a correctly running steam boiler, the water level should stay fairly constant. But when things aren’t correct, the water level can surge up and down by a substantial amount. Each downsurge can trick the automatic water feeder into adding water that’s not really needed, eventually flooding the boiler. For instance, if your water is too alkaline, with a pH of 11 or more, it will foam in the boiler and the foam will leave along with the steam, tricking the automatic feeder into adding unnecessary water. When the condensed foam returns, you get a flooded boiler.

Surge Problem

• Water surges from certain other conditions can send water up the steam risers. For instance, a surge can result from applying too much heat to the boiler, incorrect piping of the steam header above the boiler, or dirty or rusty water in the boiler. You can also get water surges from motorized zone heating valves. Normally, steam pressure combines with the weight of the condensed water to force water back into the boiler. But if a zone valve closes too quickly, it will cut off steam pressure before all the condensed water has been returned to the boiler. The automatic feeder makes up the difference. But when the zone valve opens again to admit more steam, all the left over condensed water rushes back to the boiler and floods it.

Feeder Malfunction

• A malfunctioning automatic water feeder also can cause a flooded boiler. Sediment or hard water scale can build up in the feeder, preventing the valve from closing completely. Water then continually leaks into the boiler, eventually flooding it. The problem also could be human error. If the boiler water level appears low, there’s the temptation to add water manually, rather than relying on the automatic feeder. You should never add water manually unless the boiler is off and all condensed water has returned to the system.