What I Found in the Utility Closet
I knelt down with my flashlight and started documenting. The bottom of the tank had heavy rust scale flaking off in sheets. The cold water inlet fitting was so corroded that the pipe connection looked like it was growing a tumor of greenish-white mineral buildup. But the thing that really got my attention was the TPR valve.
The temperature and pressure relief valve is a safety device. If the pressure or temperature inside the tank gets too high, this valve opens and releases water through a discharge pipe to prevent the tank from exploding. I am not being dramatic when I say "exploding." A water heater without a functioning TPR valve is essentially an unregulated pressure vessel. There are documented cases of failed water heaters launching through roofs like rockets.
On this unit, the TPR discharge pipe had been connected to a copper line that ran into the floor drain. Fine so far. But when I lifted the test lever on the valve, nothing happened. No water, no hiss of pressure, nothing. I tried again. The lever moved about a quarter inch and seized. The valve was completely frozen from corrosion and mineral buildup. It had not been tested or operated in years, possibly decades.
The Serial Number Told the Rest of the Story
I photographed the data plate and decoded the serial number. The water heater was manufactured in April 2001. That made it 18 years old at the time of my inspection. The typical lifespan for a tank water heater is 8 to 12 years. This one was running on borrowed time with a safety valve that no longer worked.
I checked the anode rod port on top of the tank. It was seized shut. I couldn't even get a socket on it because of the corrosion. That told me the anode rod had never been replaced, which meant the interior of the tank had been corroding unchecked for years. The rusty water in the drain pan confirmed it.
The Conversation Nobody Wants to Have
I brought my client, a first-time buyer named Marcus, down to the utility closet. His girlfriend Jess was there too. They had been excited about the house. Good neighborhood, good schools, within their budget. I could see the anxiety creeping in as I walked them through what I was looking at.
"So what does this mean?" Marcus asked. He was holding a notebook with a running list of things I had flagged. The water heater section was getting long.
I explained it as plainly as I could. The water heater was 18 years old, well past its expected life. The tank was actively corroding from the inside. The safety valve designed to prevent a catastrophic failure was non-functional. And the unit was located in an interior closet, which meant if it did fail, the flooding would go directly into the main living space.
Jess looked at Marcus. "How bad could it actually get?"
I told them about pressure vessel failures. A 50-gallon water heater holds water at roughly 150 degrees and 40-80 PSI of pressure. If the thermostat fails and the TPR valve doesn't open, the water superheats past boiling while the pressure climbs. At some point, the weakened tank gives way. The sudden pressure release converts superheated water to steam instantly, and the resulting expansion is violent. I have seen photos of water heaters that went through two floors and out the roof of a house.
I want to be clear that this is rare. Most water heaters just leak and make a mess. But the combination of a frozen TPR valve, severe corrosion, and an 18-year-old tank meant the risk was real and not theoretical.
What the Sellers Said
Mr. Nelson came by during the inspection. He was a friendly guy in his mid-seventies who clearly took pride in the house. When I showed him the water heater situation, he seemed genuinely surprised.
"It still makes hot water," he said. And he was right. It did. That is the tricky thing about water heaters. They keep working right up until they don't. Mr. Nelson had never tested the TPR valve, never drained the tank, never replaced the anode rod. In 18 years of ownership he had done zero maintenance on it. The unit just quietly ran in that closet, getting more dangerous every year.
He wasn't negligent. He just didn't know. Most homeowners don't. Water heater maintenance isn't something anyone teaches you when you buy a house. You turn on the faucet, hot water comes out, and you don't think about the appliance responsible for it until something goes wrong.
How It Played Out
Marcus and Jess negotiated a $2,000 credit for water heater replacement, which was more than enough. They hired a plumber I recommended, a guy named Dennis who I had worked with on dozens of post-inspection repairs. Dennis replaced the unit with a new 50-gallon Rheem for $1,350 all in. He also installed an expansion tank and a proper drain pan with a discharge line to the exterior.
When Dennis pulled the old unit out, he called me. "You gotta see this," he said. The bottom of the tank had corroded so thin in one spot that he could push his thumb through it. His exact words were "another six months and this thing would have been a swimming pool." Maybe not a rocket through the roof, but definitely a catastrophic leak that would have dumped 50 gallons of hot water into the main floor of the house.
The Numbers
New water heater installed: $1,350. Expansion tank: included. New drain pan and discharge line: included. The negotiated credit was $2,000, so Marcus and Jess actually came out $650 ahead, which they used toward a new thermostat for the HVAC system.
What could the damage have been if the old unit failed? Dennis estimated at minimum $5,000 to $15,000 in water damage to flooring, drywall, and baseboards. If the failure was catastrophic rather than a slow leak, the number goes higher. And if the thermostat had failed and the TPR valve couldn't relieve the pressure, the structural damage could have been in the tens of thousands.
What Every Homeowner Should Do
I tell this story because it illustrates something I see constantly. Water heaters get ignored. They sit in closets and basements doing their job until they become a problem, and by then the problem is expensive.
Test the TPR Valve Once a Year
Put a bucket under the discharge pipe and lift the test lever on the TPR valve. Water should flow freely and stop when you release the lever. If nothing comes out, or the lever won't move, the valve needs to be replaced. A new TPR valve costs $15 to $30 and takes a plumber about 20 minutes to install.
Fair warning: on older units that have never been tested, operating the valve for the first time sometimes causes it to drip afterward because the seat gets disturbed. Still better to know it works than to find out it doesn't when you need it.
Know the Age of Your Water Heater
Check the data plate and decode the serial number. If your tank water heater is over 10 years old, start planning for replacement. If it is over 12, consider replacing it proactively before it fails on a holiday weekend when emergency plumber rates apply. I wrote a whole guide on decoding serial numbers for different brands if you need help figuring out the date.
Look at It Occasionally
Walk over to your water heater once every few months. Look for rust, puddles, mineral buildup, or corrosion on the fittings. Sniff for gas if it is a gas unit. Listen for rumbling or popping sounds. These five-minute checks cost nothing and can catch problems early.
Marcus and Jess have been in that house for almost seven years now. The Rheem is still running fine. Marcus told me last year that he tests the TPR valve every January. He said after seeing the state of the old one, he will never skip it.