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Cast Iron Radiators Leaking cracking or Burtsing

leebfree Member Posts: 2
The Perfect storm to a Broken Radiator

I recently had an experience where one Cast Iron Baseboard radiator sprung a leak, Then another.

The pressure Gauge on my OIL fueled Boiler showed normal.

If your experiencing Cracked, Leaking, or Failed Radiators check these Items:

Check your Temperature & Pressure emergency vent valve. These are USUALLY corroded and not working. This wont create an over pressure scenario in your boiler but since this valve wont open the pressure goes to the weakest spot. Your cast Iron Radiators. Replace this Valve. They cost about $25 and are easily accessed on the exterior of the boiler.

Also check your Pressure & Temperature Gauge on your furnace. In my case the temperature portion was working perfectly but the pressure gauge portion was stuck at a value that indicated normal. Yet when the boiler was shut off the indicated pressure did not change. Although this pressure gauge did not cause an over pressure condition. It really caused a problem trouble shooting. as it kept telling me my boiler was not in over pressure when in fact it was. This Gauge replacement was about $25 for the gauge and its easy to change from the exterior of a boiler.

Now we get to what really caused the over pressure condition resulting in cracked radiators. When Water is heated it expands. In a closed system of water running in radiators this expanded water must go somewhere. In most cases it should go in to an expansion tank. This tank hold some water and mostly AIR and is a AIR Tight container. As the water is heated and expands it flows into this Expansion tank, compressing the air in the tank. The water expands into the tank and the compressed air push back on the water so as the water Shrinks when it cools it leaves the expansion tank and goes back to the radiator circuit.

IF you have leaking , new leaks or cracks in a radiator I would recommend checking these 5 things
Is Emergency relief Valve Free of corrosion and working properly
Does Pressure and Temperature Gauge function properly and show a change from a cold boiler to a Boiler in operation
Is valve to Expansion tank open and operating correctly
Does expansion tank have proper amount of water and AIR
Is expansion tank leaking? Is it air tight and holding compression
At the end of the day;

if your seeing any damage to radiators. Make sure boilers expansion tank is function properly AND your boiler is operating at the correct pressure and temperatures.
Generally about 10 to 20 pounds of pressure and 180 to 210 in temperature however that does vary boiler to boiler and application to application to check your system specifications.


  • Jamie Hall
    Jamie Hall Member Posts: 23,442
    With that lack of maintenance, you're just lucky you didn't blow the boiler to kingdom come.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,076
    Were your BB rads ever frozen?