Buying a house is the biggest check most people ever write, and the plumbing is one of the easiest places to get blindsided after you've already got the keys. A standard home inspection is a mile wide and an inch deep — inspectors glance at the plumbing, but they're not crawling the sewer line or pressure-testing the supply pipes. That's where the expensive surprises hide.
We get called out to brand-new homeowners all the time who just discovered a $12,000 sewer problem their inspection never mentioned. So here are seven plumbing red flags that inspectors routinely miss or downplay — and why spending a couple hundred bucks before closing can save you tens of thousands after.
Red Flag #1: Galvanized Supply Pipes
If the home was built before 1980 and hasn't been repiped, there's a strong chance it still has galvanized steel supply lines — and that's the red flag we find most often in older Escondido, La Mesa, and El Cajon homes. Galvanized pipe rusts from the inside out, slowly choking off water flow and eventually leaking.
A home inspector might note "galvanized pipes present" and move on, but they won't tell you how far gone they are. The tells are low water pressure, rusty water in the morning, and visible corrosion at threaded joints under sinks and in the garage. Whole-home repiping runs several thousand dollars, so this is a real number to factor into your offer.
A magnet sticks to galvanized steel but not copper — a quick way to check exposed pipes yourself during a showing.
Red Flag #2: Polybutylene Pipes (1978–1996)
Polybutylene is a gray (sometimes blue) plastic pipe used widely from the late 1970s into the mid-1990s, and it's a ticking clock. It reacts with the chlorine in municipal water, gets brittle from the inside, and fails suddenly — often without warning.
Insurance companies don't love it, and some won't write a policy on a home that still has it. Inspectors frequently note its presence without flagging how serious it is. If you see gray plastic supply pipe stamped "PB2110," budget for a repipe and use it as a negotiation point.
It's less common in San Diego than galvanized, but it's out there in homes from that era. If you spot it, take it seriously — a polybutylene failure can flood a finished room before you ever see it coming.
Red Flag #3: Cast Iron Sewer Laterals Near the End
Homes from before the 1970s often have cast iron or clay sewer laterals, and after 50-plus years they're cracking, corroding, and getting invaded by roots. This is the one that bites hardest because it's completely invisible to a standard inspection — the inspector never sees inside the pipe.
A failing sewer lateral is a $5,000 to $15,000 repair, and you won't know it's failing until it backs up into the house. The only way to catch it before closing is a sewer camera scope, which we'll come back to because it's the most important thing in this article.
Our sewer line service page covers what a failing lateral looks like and the repair options, including trenchless methods that save the yard.
Red Flag #4: An Aging Water Heater
Inspectors note whether a water heater works, not how much life it has left. A tank water heater past 8 years is on borrowed time, and in San Diego's hard water — especially hot inland areas like Santee and El Cajon — many don't make it past 8 to 10.
Check the serial number on the label; most brands encode the manufacture date in it. If you're buying a home with a 10-year-old tank, assume you'll be replacing it soon and factor $1,200 to $2,500 into your plans. Also check that it has current code items — seismic strapping, an expansion tank, a drip pan — because missing those means an unpermitted install.
An undersized or aging heater isn't a deal-breaker, but it's a real cost you'd rather know about before you own it.
Red Flag #5: Slab Leak Signs Hiding in Plain Sight
Slab leaks — leaks in pipes under the concrete foundation — are common in San Diego homes from the 1960s through 1980s, and the early signs are subtle enough that a quick walkthrough misses them. Warm spots on the floor, faint moisture, a musty smell in one room, or hairline cracks in flooring can all point to a slow slab leak.
A seller may not even know, or a fresh coat of paint might be hiding old water staining. If you notice any of these signs, get a leak detection inspection before closing — our leak detection and repair team can confirm or rule it out without tearing anything up.
Slab leaks are especially worth checking in older Escondido and La Mesa homes built on concrete slabs, where we find them regularly.
Red Flags #6 & #7: No Pressure Regulator, Wrong-Sized Heater
Two more that inspectors gloss over. First, a missing or failed pressure regulator (PRV). San Diego's incoming water pressure can run high, and without a working PRV your future plumbing takes a beating — and you'll be replacing fixtures and dealing with leaks sooner. A PRV is cheap to add or replace, but you want to know going in.
Second, a water heater that's undersized for the home. A 40-gallon tank in a five-bedroom house means cold showers and a unit that's constantly overworked and failing early. Match the heater to the household, and if it doesn't match, that's another planning item.
None of these are necessarily deal-breakers — they're just things you'd rather know before you own them than discover the first month in.
The Move That Saves Thousands: A Pre-Purchase Inspection
Here's the bottom line. A separate plumbing inspection plus a sewer camera scope — the scope runs about $199 — is the single best money you can spend before closing on an older San Diego home. The scope alone has saved our clients from buying houses with collapsed sewer lines they'd have inherited blind.
If we find problems, you've got leverage. You can ask the seller to make repairs, credit you at closing, or knock the cost off the price. Sellers expect some negotiation after inspections, and a documented sewer or pipe issue is hard to argue with — it's on video.
We do pre-purchase inspections across San Diego County — Escondido, Santee, El Cajon, La Mesa, La Jolla, and everywhere between. For a few hundred dollars, you walk into the biggest purchase of your life knowing exactly what the plumbing's going to cost you. That's peace of mind worth paying for.
Buying a home and want the plumbing checked before you close? Call Pipe Dream Plumbing Co. at (858) 215-1199 for a pre-purchase inspection and sewer scope. We serve Escondido, Santee, El Cajon, La Mesa, La Jolla, and all of San Diego County.