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Steam is coming out of the condensate- or boiler-feed receiver vent

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Published
July 10, 2009 Subscribe to RSS feed

The steam traps have failed in the open position.
Besides causing water hammer and uneven heating throughout the building, steam will show up in the vented receiver when the traps fail. As the condensate gets hotter, the condensate- or boiler-feed pump will begin to cavitate. Before long, the pump can't move the water, and the receiver overflows.
Find the failed traps and repair or replace them.

There's a "master" trap at the inlet to the condensate pump.
When steam traps fail in the system, the returning condensate will be too hot for the condensate pump to handle. Some contractors who are unfamiliar with steam heating systems will try to solve this problem by installing a single "master" trap at the inlet to the pump's receiver. This creates problems because the return lines are now double-trapped. The flow of condensate back to the boiler will slow, and the boiler will begin to cycle erratically or flood.
Remember, the steam traps are in the building to create the points of pressure and no pressure. If the system could operate with a single "master" trap, the Dead Man who installed the system would have done it that way.
Another problem with a "master" trap is that it will release condensate at steam temperature. Much of that hot condensate will flash back into steam as it enters the receiver, causing further problems with the pump.
Remove the "master" trap, and repair the defective traps throughout the system.

The steam traps are oversized.
If you base the size of the two-pipe steam trap on the size of the line, you will almost always oversize the trap. An oversized trap will barely open when the condensate reaches it. Since the pin sits so close to the seat of the barely opened trap, the condensate will flow across the seat at high velocity. Condensate contains bits of rust and sediment, which quickly wear down the seat, keeping the trap from shutting tightly. Trap manufacturers call this process "wire drawing," and it's a very common cause of trap failure.
Check the size of the trap against the load and the pressure differential. If it's oversized, replace it.