You watched the video. You found the right RP number. You pried off the little red-and-blue button, got the set screw out, wrestled the old cartridge free, and dropped the new one in.

You turned the water back on.

And it’s still dripping.

That’s a genuinely frustrating place to be. You did the repair everyone said would work, you’re out the cost of the part and most of your Saturday, and the faucet is doing exactly what it did before you started.

Here’s the good news: you almost certainly didn’t do anything wrong. On an older Delta faucet, the cartridge often isn’t the part that was leaking in the first place.

If you haven’t taken your faucet apart yet and you’re just trying to stop a drip, start with our general guide to repairing a leaky faucet instead. This post is for people who already tried.

First, where is the water actually coming from?

This is the step almost everyone skips, and it’s the reason a lot of cartridge replacements fail. Three different leaks look similar from across the kitchen, and they have three completely different causes.

Watch your faucet for a minute and figure out which one you have.

If you replaced your cartridge because of leak #1 and it’s still dripping, keep reading. That’s the one where the cartridge is usually innocent.

Why the new cartridge didn’t stop the drip

There are parts underneath the cartridge you probably didn’t replace

This is the big one, and it’s the thing most repair guides leave out entirely.

On a lot of Delta faucets — especially the older single-lever ball-style ones and two-handle models — the cartridge or ball isn’t what actually seals off the water. Sitting below it are two small rubber seats with a spring under each one. Those rubber seats press up against the ball or stem, and that is the seal that stops your water.

The seats and springs are a cheap part (Delta’s kit is RP4993 on many models). They’re also the single most common reason a Delta faucet keeps dripping after a cartridge or ball replacement.

The valve seat is the part you can’t buy

Here’s where it gets less fun.

Underneath those rubber seats is a brass surface machined into the faucet body itself. That’s the valve seat. It has to be smooth for anything to seal against it.

Over years, mineral buildup does two things to it. It coats the surface, and it slowly pits and roughens the brass underneath. Once that surface is scored, no cartridge will ever seal against it — you can install a brand new one every month and it will drip every time.

If you’re in the GTA, this is not a rare failure. It’s the normal end of life for a faucet here, and it’s driven almost entirely by water quality — hard water quietly wears out fixtures across Toronto homes years before people expect it to.

A piece of the old seal might still be in there

When a cartridge has been in place for fifteen or twenty years, it doesn’t always come out in one piece. The bottom gasket or a chunk of old rubber can stay behind in the valve body while everything else comes free.

You then seat a new cartridge on top of that debris. It sits slightly high, or slightly crooked, and it leaks.

Delta’s own instructions call this out — the bottom gasket is supposed to come out with the cartridge. If you didn’t specifically check for it, take another look. Reach in and feel the bottom of the valve body. Anything soft or crumbly in there needs to come out.

You may have the wrong cartridge

Delta makes a lot of faucets, and the internals are not interchangeable.

Diamond Seal (DST) kitchen faucets, Monitor 1300/1400 series shower valves, MultiChoice valves, and older ball-style faucets all take different parts. Common cartridge numbers include RP50587, RP73000 and RP60114 for DST models, and RP46074 for 1300/1400 series shower valves — but the only way to be sure is to find your faucet’s model number and check the parts diagram.

Two things go wrong here regularly:

• Someone at the big-box store picks the part for you. They’re guessing based on a photo on your phone. Sometimes they’re right.
• You bought a knockoff online. Third-party Delta-style cartridges are everywhere and they’re cheap. The tolerances are slightly off and the rubber is softer. It’ll fit. It’ll install. It just won’t seal properly, and you’ll conclude the repair failed when really the part did.

Delta covers most repair parts under a lifetime warranty and will send replacements to the original owner at no charge, so it’s worth checking before you buy anything at all.

Try the free fix first: flush the line

Before you assume a part failed, rule out debris. Delta recommends this as step one and it costs nothing.

Shut off the water supplies. Remove the aerator or spray head. Move the handle to the fully-on, full-mix position. Turn the supplies back on and let it run for a minute to push any sediment out of the valve body. Rinse the aerator, put it back on, shut the water off with the handle.

If the drip stops, you had grit sitting on a sealing surface, not a worn part. It happens more often than you’d think, especially after work has been done on the water main nearby.

Before you open it up again, test your shut-off valve

This is the warning we most wish homeowners got before they started.

In older GTA homes, the shut-off valves under the sink have often sat untouched for twenty or thirty years. When someone finally cranks one hard, the stem seizes, the packing fails, or the valve simply won’t close all the way anymore.

Now you have two problems. The faucet still drips, and you can’t isolate the water to work on it.

That’s how a slow drip becomes an emergency call at 11pm — not because the faucet got worse, but because the only thing standing between you and running water gave out mid-repair.

And if it’s already happened to you, here’s the rule our plumbers use:

Knowing which situation you’re in saves you a lot of panic at midnight.

The honest answer: on an old faucet, stop repairing it

We’d rather tell you this plainly than have you spend another three weekends on it.

When our plumbers arrive at a home where the homeowner already replaced the cartridge and it’s still dripping, most of the time the recommendation is to replace the whole faucet — not to keep chasing parts.

Not because repair is impossible. Because on a faucet that’s old enough to have a pitted valve seat and hardened seals, you’re repairing one worn component inside an assembly where everything is the same age. You fix the drip, and four months later the O-rings go, or the handle gets loose, or it starts weeping from somewhere new.

Look at the actual math. You’ve already spent on one cartridge. Add a seats-and-springs kit. Add a second cartridge when that doesn’t work. Add a service call when you finally give up. You’re now well past what it would have cost to put in a faucet that comes with a warranty and won’t need touching for another fifteen years.

What it costs in the GTA

Straight numbers, so you can decide before anyone comes out.

We supply the faucet as part of the job, so you’re not standing in an aisle trying to work out which model has a brass body and which one is plastic underneath the finish. You get one flat-rate price for the whole thing before we start.

That’s the real comparison. Not $40 versus $400. It’s repeated $40 parts, plus your weekends, plus an eventual service call — against one job that ends the problem.

When to call us

Call right away if:

• You can’t shut the water off, or water is running where you can’t stop it
• The shut-off valve under the sink failed while you were working
• You’ve now got a leak in the cabinet as well as at the faucet

Book for the next available day if:

• The handle closes and you’re down to a slow drip
• You’re on your second cartridge and it’s still leaking
• The faucet is 15+ years old and you’d rather replace it than keep repairing

DrainRooter Plumbing has been serving Etobicoke, Toronto, Mississauga, Oakville and Brampton for over a decade. Licensed and insured, upfront flat-rate pricing, one-year labour warranty, and we’re open 24/7 — nights, weekends and holidays.