Home Inspection Water Heater: What Inspectors Check

The water heater is the hardest-working appliance in a home, heating water every day for showers, laundry, and dishes — and it is one of the most common sources of inspection findings. Knowing what a home inspection water heater check covers helps buyers understand the report, price a replacement, and spot safety defects before closing. This guide walks through every check an inspector performs on a water heater, what each finding means, and what it costs to fix.

How Inspectors Determine Water Heater Age

The first thing an inspector does at a water heater is read the rating plate. Every water heater has a metal label — usually on the side of the tank — that lists the manufacturer, model number, serial number, capacity in gallons, and fuel type. The serial number encodes the manufacture date, and most inspectors can decode it on the spot. Rheem, AO Smith, Bradford White, and other major brands all use serial-number date codes, though the format varies by brand. If the rating plate is missing or unreadable, the inspector notes the age as unknown and recommends further evaluation.

Age matters because it predicts remaining life. Standard tank water heaters last 8 to 12 years. Gas units tend to last slightly longer than electric units, and water quality plays a large role: hard water and sediment shorten tank life, while soft water and regular flushing extend it. Tankless water heaters last 15 to 20 years. A heater that is 6 years old with no visible problems is a normal finding. A heater that is 14 years old is a near-term replacement, even if it is still working — the risk of a tank failure rises sharply after year 12, and a tank failure means 40 to 50 gallons of water on the floor.

Inspectors also check the installation date against the permit history when it is available. A water heater replacement should have a permit on file in most jurisdictions. A permitted, documented replacement is a selling point; an unpermitted replacement is not automatically a problem, but it means no inspector verified the venting, gas connections, or T&P discharge line. If the heater looks new but there is no permit, ask the seller for the installer's invoice.

Tank Condition and Rust

The inspector examines the outside of the tank for rust, corrosion, dents, and signs of past or present leaks. Rust at the base of the tank is the most serious visual finding — it usually means the tank itself is corroding from the inside, and a tank that leaks from the body cannot be repaired. Rust on the pipe connections is less alarming but still worth noting, because corroded connections eventually leak.

Water pooling at the base of the heater is a red flag that demands immediate attention. It may be condensation (common in humid basements and usually harmless), a leaking T&P valve, a loose connection, or a failing tank. An inspector who finds water at the base will try to identify the source and will recommend a plumber's evaluation if the source is not obvious. Never dismiss a puddle at a water heater as "just condensation" without checking — the difference between condensation and a tank leak is the difference between a $0 finding and a $2,000 replacement.

Inspectors also look for sediment damage. In areas with hard water, sediment builds up in the bottom of the tank, causing rumbling or popping sounds when the burner fires and reducing efficiency. A heater that rumbles loudly is working harder than it should and is closer to failure. Regular flushing extends tank life, but few homeowners do it, so sediment is a common finding on older heaters. Our how long water heaters last guide covers lifespan by type and what shortens it.

Venting and Combustion Safety

On gas water heaters, venting is a safety issue, not a cosmetic one. The flue carries combustion gases — including carbon monoxide — out of the house. An inspector checks that the vent pipe rises steadily to the chimney or exterior vent with no sagging sections, that it is the correct material and diameter, and that all joints are secure. A vent that sags, disconnects, or is made from the wrong material can spill carbon monoxide into the home.

Backdrafting is the most dangerous venting defect. It happens when exhaust gases flow backward out of the draft hood instead of rising up the flue — usually because of a blocked flue, a competing exhaust fan, or a house that is too tightly sealed. Signs of backdrafting include scorch marks, melted plastic, or soot around the draft hood, and a failed draft test. Inspectors test for backdrafting by holding a smoke pencil or a lit match near the draft hood and watching whether the smoke is drawn up the flue or pushed back into the room. A heater that backdrafts is a safety defect that should be fixed before closing, full stop.

Power-vented and direct-vent heaters have their own checks: the inspector confirms the vent terminates in the correct location, that the blower operates, and that the condensate drain (on high-efficiency condensing units) is properly routed. A condensate drain that dumps into a wall cavity or onto the floor is a defect.

The T&P Relief Valve

The temperature and pressure (T&P) relief valve is the most important safety device on a water heater. If the thermostat fails and the tank overheats, or pressure builds beyond safe limits, the T&P valve opens and releases hot water to prevent the tank from exploding. It is a simple device, and when it is installed wrong, it is a serious safety defect.

Inspectors check three things about the T&P valve. First, that it exists and is installed in the correct location, on the top or upper side of the tank. Second, that the discharge pipe is the right material (usually CPVC or copper, never PVC, which softens at high temperatures) and the right size, typically three-quarter inch. Third, and most commonly failed, that the discharge pipe terminates correctly: it should run downward, end 6 inches above the floor or drain outside the building, and never be capped, plugged, or routed into a wall cavity.

Common defects include a discharge pipe that ends inside a wall (so a release floods the wall cavity invisibly), a pipe that terminates more than 6 inches above the floor (scalding risk), a pipe with an uphill section (which traps water and prevents the valve from draining), and a missing discharge pipe entirely. Inspectors also test the valve by lifting the lever briefly — water should flow out and stop when the lever is released. A valve that drips continuously, will not open, or will not reseat needs replacement, a $150 to $300 job.

A T&P valve defect is one of the few plumbing findings that inspectors describe as a safety hazard rather than a maintenance item. If the report flags it, treat it as a must-fix before closing, not a someday project. A water heater tank that cannot relieve pressure is a genuine explosion risk — rare, but catastrophic when it happens.

Water Connections and Shutoff Valves

The inspector checks the cold water inlet and hot water outlet connections for leaks, corrosion, and correct installation. Flexible connectors — braided stainless steel or corrugated copper — are standard and should be free of kinks, rust, and deterioration. Rigid connections should be properly supported. Dielectric unions, which prevent galvanic corrosion where copper meets steel, should be present at the tank connections in a mixed-metal installation; their absence is a common minor defect that shortens the life of the connections.

A shutoff valve on the cold water inlet is required in most jurisdictions and is essential for servicing the heater. The inspector checks that it exists and operates. A seized or missing inlet valve is a minor repair, but it means the heater cannot be isolated without shutting off water to the whole house.

The inspector also looks for an expansion tank on closed plumbing systems. When a home has a pressure-reducing valve or a backflow preventer, the plumbing system is closed, and heated water has nowhere to expand. An expansion tank absorbs that pressure. Without one, the T&P valve may drip, and the system experiences repeated pressure spikes that stress every connection. Many older homes lack expansion tanks; adding one costs $150 to $400 and is a standard part of a modern water heater installation.

Tankless Water Heater Checks

Tankless (on-demand) water heaters have no tank to rust, but they have their own inspection checklist. The inspector checks the gas line size first, because tankless units demand far more gas than a tank heater — typically 150,000 to 200,000 BTU versus 40,000 BTU for a tank unit. An undersized gas line is the most common defect on tankless retrofits: the unit works at low demand but shuts down or delivers lukewarm water when multiple fixtures run. The fix is a larger gas line, which can cost $500 to $2,000 depending on the run.

Venting is checked next. Tankless units use sealed combustion with dedicated venting — usually PVC or stainless steel, depending on whether the unit is condensing or non-condensing. The inspector confirms the vent material matches the manufacturer's requirement, the vent terminates in an approved location with proper clearances from windows and doors, and the condensate drain on condensing units is routed to a drain. A condensing unit without a condensate drain, or with a drain that empties onto the floor, is a defect.

Scale buildup is the tankless equivalent of sediment. In hard-water areas, mineral scale coats the heat exchanger, reducing efficiency and eventually causing error codes and shutdowns. Inspectors look for evidence of descaling maintenance — a service valve kit on the unit is a good sign — and note whether the unit shows error codes or signs of overheating. Annual descaling is recommended in hard-water areas and costs $150 to $300 from a plumber.

Common Defects and What They Cost

Here are the water heater defects inspectors find most often, and what each one typically costs to fix in 2026:

When the report comes back, prioritize safety defects first. A T&P discharge problem, a venting defect, or backdrafting should be corrected before closing, or credited so you can fix it immediately after. A heater that is simply old is a budgeting item, not an emergency — but it should be reflected in the price you pay. Get a plumber's written estimate for any flagged item, and use it in your negotiation.

If you are buying a home and the water heater is the only flagged item, you are in good shape. A $1,500 to $2,500 replacement is a normal cost of homeownership, and a new heater with a warranty is a genuine upgrade. The problems worth worrying about are the ones the heater reveals about the rest of the system — corroded supply lines, a missing expansion tank, or a gas line that cannot support a modern unit. Those are the findings that turn a simple appliance replacement into a system repair, and they are exactly what a good inspection is designed to catch. For the full plumbing picture, start with our plumbing inspection checklist and the home inspection hub.