Zero Pressure on Boiler

RSGlass

I have an old boiler (circa 1925) that shows a zero pressure reading when it's not operated, but normal (about 15) when the thermostat is turned on. I don't think the zero pressure is due to a leak, because adding water makes the pressure skyrocket. So the water level seems to be correct, the radiators have been bled, and pressure continues to drop to zero once the thermostat switches the boiler off. What's theh problem?

Ken_8

The expansion tank

is "flooded" and lost its capacity to maintain system pressure in the typical range of 12 # cold - 20 # hot.





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RSGlass

expansion tank flooded fix

What's the fix when the expansion tank is "flooded"? Is this easy to correct?

Mike T., Swampeast MO

Is it the old plain tank? They're usually painted black or silver, quite long and are hanging between a couple of floor joists near the boiler.

The other type is more modern, frequently gray (you might have more than one on a big old system) and you'll see an air fitting (like a tire) on one side.

Which do you have?