On Friday, October 24, 2014 5:41:02 AM UTC-6, trader_4 wrote:
On Thursday, October 23, 2014 7:42:48 PM UTC-4, Stormin Mormon wrote:
On 10/23/2014 3:20 PM, wrote:

These things blow up all the time and KILL people.


Boiler explosion:
https://www.youtube.com/watch?v=fCej2OQSKnY

This is a commercial boiler explosion but residential explosions are just as bad.


I'll admit, I've never heard of a residential boiler
explosion. How many occur in the US each year? Any
proof of this?

-


Yes, that's a good question, isn't it? I'm sure they occur,
but I've never seen, heard of, or even read about one, so I'd
bet they are relatively rare.

Plus, if he read the thread, the OP identified what was wrong
with the boiler. The expansion tank had failed and it's been fixed.
Finally, like others here have posted, I've seen TPR valves that
once opened, won't fully close again and have a small leak. Over
years, they get slightly corroded, crud in them, etc. And if it's
dripping, I don't see the harm in replacing it with a new one and
see what happens. If the leak stops, it's the valve. If it continues,
then either diagnose further yourself, or call a plumber. How
exactly is a boiler going to blow up if it has a new TPR valve on it?

Yes, Pressure Relief valves are designed to open and close as needed. If you have particularly hard water then calcium or what ever can build up and stop a PRV from seating properly again and it should be replaced.

How is a boiler going to blow up if it has a new PRV? Boilers pump water around what is essentially a closed loop. Included in this loop are things like the heat exchanger, air scoop, thermal expansion tank and Pressure Relief valve.
This loop should have a maximum of 20 pounds of pressure in it. Your PRV opens at 30 PSI.
Air can enter this loop in a number of ways and ideally it is removed by the air scoop. Lets say you have a leak and air is entering the system. Over a number of days air builds up but is not removed because of a faulty air scoop. This air slowly makes its way around the loop causing pockets of air that grow in size as they come together. A pocket of this air hits the heat exchanger and 200,000 BTUs of heat energy from the burner causes the air to expand very quickly causing a pressure spike. Ideally your PRV burps and releases this pressure and your thermal expansion tank absorbs some as well..
Lets say some of this mineral buildup that clogs PRV valves gets lodged in the PRV causing a small restriction. Air hits heat exchanger again and causes TPR to burp again causing some more mineral buildup. A few days later the air bubble has grown some more. Its cold and the boiler has been running at 100% for a few hours. The large air bubble hits the heat exchanger again and expands very quickly.
Now at this point there does not have to be a cataclysmic explosion where half the house blows up. You might just hear a small ping as the heat exchanger cracks. All that instant pressure has to go somewhere and scolding hot steam and water shoots out as Mrs Jones walks by carrying her laundry.
Maybe nobody is around and the boiler purges steam, the high limit safety switch malfunctions and the burner does not turn off causing a fire.

This is just one possible scenario, there are many others.