Although it is rare, tank-based water heaters and boilers can (and do) explode, often with disastrous results. Water heaters and boilers are built to be safe and are found in millions of homes across the United States. Failsafe devices are built into water heaters and boilers to prevent dangerous pressure levels from building up inside the devices. However, the failsafe devices occasionally fail.
A pressure-and-temperature valve is the failsafe for a water heater or boiler (PT valve). Some people refer to them as T & P valves, but they are the same thing. The valve is usually located on or near the top of the water tank or boiler and is designed to open when a certain pressure or temperature is reached inside the tank. Some tanks have a pressure valve that opens only when higher pressure is detected, regardless of tank temperature.
According to basic physics, temperature and pressure in a closed system have a direct relationship. That is, as temperature rises, so do pressure, and vice versa. Increase the pressure in the system by increasing the temperature of your hot water tank or your boiler control.
These heating systems are intended to handle "modest" temperature and pressure changes. Manually raising the temperature on your water heater or boiler should never result in disaster.
So, what could possibly go wrong? It's usually a combination of factors!
Regulators and thermostats are used to keep a device's operating temperature within a specific range. When the temperature falls below the set point, the regulator activates the heater, which heats the water in the system. When the temperature reaches the maximum allowed by the regulator, the heat is turned off. If the system's regulator or thermostat fails, one of two things can happen no heat at all or constant heat!
If the regulator or thermostat seems to become "on" and continuously heats the system, the T & P valve or pressure valve is supposed to open and relieve pressure in the tank. Its purpose is to keep the tank from ever reaching the point where an explosion is likely.
Now for the bad news. T&P and pressure valves can both fail. Unlike a regulator or thermostat, where erratic behavior indicates a problem, there is no way to tell if a PT valve is bad or has failed without testing it. Testing is easy, and homeowners should check the PT valves on their water tanks every month or two.
The valve can be manually lifted or flipped into the "open" position. The valve is still doing its job if it opens and closes smoothly. It should be replaced if it does not open or only opens and closes with difficulty. PT valves on boilers and water heaters should be replaced every three years, regardless of whether they are working or not. A PT valve is a low-cost item that provides priceless peace of mind.
Don't underestimate the amount of harm a faulty water heater can cause to your home. A water heater or boiler can generate more than 100,000 pounds of pressure before exploding, depending on its size. An exploding tank can lift off its base at 350 MPH and easily shatter a home's foundation, floors, and roof. A fully pressurized 50-gallon water tank can reach an altitude of more than 500 feet if not obstructed!
Approximately 40 or 50 gallons of potentially scalding hot water are contained in a hot water tank. Then there's gravity to consider: what goes up must come down! An empty water tank can weigh between 75 and 200 pounds, and when it returns, it may be in one piece or in several pieces.
HVAC experts from Home Mechanics can assist you with routine maintenance on your hot water tank and/or boiler, demonstrate how to test your PT valve, and provide valve replacement services as needed. Water heaters and boilers can be used safely in the home, but they do require professional inspections and maintenance on a regular basis.
To schedule an appointment, please call (978) 539-7172 at any time. Call us if your water heater or boiler is not working properly, including over- and under-temperature conditions, as well as a pilot light or electronic ignition issues.
Home Mechanics provides premium quality water heaters and combi-boilers from one of the market's leading brands. On-demand tankless water heaters from Navien and Rheem are among the best in the industry.
Read more about how different heating systems work.