Relief Valve

Potable water boilers, water heaters and storage tanks are limited to a maximum temperature of 210°F. Most of them supply water in the range of 120 to 140°F. Therefore they can make use of pressure-temperature type relief valves for overpressure protection.

The pressure-temperature relief valve provides an extra level of safety in helping to eliminate the steam explosion hazard. Temperature controls (limit switches, gas valves, heating element thermostats, etc.) need to be regularly checked and properly maintained.
But pressure-temperature relief valves can back up temperature limit controls in the event of control malfunction, runaway firing conditions, corrosion and pressure transients.

Regardless of the safety valve type, they need to be installed correctly and tested annually. With a little bit of attention to this equipment, we can all look forward to an uneventful and pleasurable hot shower- especially critical for those of us who need reviving some mornings!

How can I tell if my water heater is at risk of exploding?

As we mentioned, most water heaters operate safely 24 hours a day, 365 days a year. Here are some simple guidelines and warnings for water heater safety:

If it's been more than a year since you Temperature - Pressure relief valve has been tested you should test it. T & P valves are mechanical devices which means that they can fail or clog.

This device is your last line of defense in case of a thermostat failure resulting in overheating of your tank.

It does not matter how old your water heater is. The tank in our video was purchased new just for this demonstration.

Sputtering and spewing from your faucets as you turn them on could be a sign of your water heater overheating. This is especially true if the water heater has been sitting idle for a while.
The spewing/sputtering can occur on either the hot or cold side of your faucet.

Excessively hot water is a sign of a thermostat malfunction, a precursor to excessive pressure build up.

A dripping or trickling T&P valve can mean that your water heater is overheating or over pressure.

What made the water heater explode in the video?

We used a new, 12 gallon water heater (typically, water heaters in homes are at about 4 times this size)

For heating, we used a standard, 4500 watt heating element.
We began with 0 (zero) pounds of pressure.
Could also have used a Natural Gas water heater . It does not matter what heats the water; gas, L.P. gas, electric or oil.

Typical homes have between 40 and 80 pounds of pressure.
As water heats, it expands which results in a pressure increase.

In our demonstration, it took about 1 1/2 hours to rise from 0 to 410 psi which is the pressure at which the tank exploded.
The water temperature was about 400 degrees.

When the tank ruptured, the water erupted into a steam explosion.

These are the same conditions that could exist if your thermostat became stuck "on" and your T&P was faulty.

Is there a bomb in your home?

Because of built in safety devices most water heaters safely operate day in, day out without any major problems. But don't let the excellent safety record of water heaters lull you into forgetting about the explosive potential of these marvels of convenience. When a water heater explodes, it releases a tremendous blast force which can easily demolish a building.

Click here to watch the video of the water heater blast.

April 25, 2009
LOWELL, Mass. -- A Lowell family was jolted from their beds early Saturday morning after their hot water boiler exploded in their home, leaving a gaping hole in the side of their house.

Firefighters said homeowner Areti Tsakalakos and her husband and daughter are lucky to be alive.

“It was a big boom like the house came down, I thought there was an earthquake,” she said. “It's a mess in there.”

The hot water boiler exploded shortly after 7 a.m., Lowell Fire Department Chief John Dowling said.

“The boiler is blown apart. Pieces of it are mi ssing the sides have been blown out, so it's pretty obvious the boiler caused the explosion,” he said.

The blast was so powerful it knocked over a water heater, ruptured gas pipes and blew out the garage. Firefighters were forced to evacuate four other neighborhood houses.

“It essentially blew the right side of this house off its foundation,” Dowling said. “The back wall's been blown out the side wall's been blown out the garage doors in pieces.”

Inspectors said in most cases, boilers blow straight up, but the boiler in the Tsakalakos home blew sideways. Upstairs is where the family had been sleeping.

“Thank god thank god for that,” Areti Tsakalakos said.

Building inspector David St. Hilaire said he believes the real relief valve on the boiler malfunctioned.

“It's similar to a pressure cooker it builds up pressure and when it reaches a certain temperature if the boiler doesn't shut down it releases,” he said.

Inspectors will examine the boiler further on Monday, but for now the Tsakalakos family, who lived in their home for 37 years, is homeless. Copyright 2009 by TheBostonChannel.com.