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A Troubleshooting Guide for a Peerless Cast-Iron Boiler

Victoria Lee Blackstone

The National Board of Boiler and Pressure Vessel Inspectors reports that cast-iron boilers experience few problems. The Peerless Company makes cast-iron boilers that have a stellar industry reputation, according to eLocalPlumbersBlog.com.

Cast-iron boiler burners should produce blue flames.

Although problems may be infrequent, troubleshooting cast-iron boilers considers three common problems: cracking, leaking and faulty pilot lights.

Hydronic Heating

In a hydronic heating system, cast-iron boilers use water or steam to produce heat instead of warmed air. Heat is not forced through ducts, which eliminates the need for blowers and fans, but is moved through sealed pipes by radiation or convection, according to Peerless. When working properly, boilers rely on pilot lights that remain lit to ignite burners, which supply heat to the unit. Because hydronic heating systems are sealed, moisture should not leak from the system.


The National Board of Boiler and Pressure Vessel Inspectors reports that the primary problem of cast-iron boilers is cracking. When a boiler becomes dirty, sludge can accumulate in the bottom and can hinder circulation within the system. This can cause the boiler to overheat, which can cause it to crack. If the water level in a boiler becomes low, this can also cause it to overheat. In an attempt to raise the water level and cool the water in an overheated boiler, some people add cold water; however, this can also cause the boiler to crack.

Leaking Water

Cast-iron boilers have relief valves that open to release water from the system. One reason for leaking water is an undersized expansion tank that is insufficient to control water pressure. At the expansion tank, the cold-water supply line is connected. Leaks can also occur if the supply line is connected improperly or in the wrong place, according to Peerless. When cast-iron boilers are assembled, sections are sealed together. Using chemical treatments in your boiler will deteriorate these seals and cause leaks, according to FacilitiesNet.com.

Pilot Light

Peerless offers troubleshooting tips for why pilot lights do not remain lit. Drafts near boilers from windows or doors (even garage doors opening and closing) can extinguish the pilot light. If your boiler is near your clothes dryer, the dryer vent could leak air that is directed toward the pilot light. If you have other gas appliances with pilot lights that also go out, it could point to a system problem with obstructed gas flow or improper piping. If all these areas are problem-free, check the thermocouple or the gas valve for malfunction.