The smell hit me before I even stepped into the bathroom—damp earth, faintly sour, like forgotten laundry left in a washing machine. Not sewage, not quite mould, but that insidious middle ground where water’s been lingering just long enough to breed trouble. I’d been called in to fix a slow-draining shower, the kind people put up with for months, pouring bleach down the drain like it’s a ritual. But when I knelt and tugged the grate, the whole flange shifted under my fingers. Not loose. Dead. The PVC had cracked at the base, the threads stripped from years of overtightened screws, and the mortar bed beneath had turned to mush. This wasn’t a clog. It was a structural failure hiding in plain sight.
This guide focuses on flange replacement. For comprehensive installation procedures, see our complete shower drain installation guide.
Most homeowners think a leaking drain means a new seal or a fresh wax ring—fine for toilets, irrelevant here. The shower drain flange is the anchor. It’s bonded to the pipe, embedded in the subfloor, and sealed beneath your tile. When it fails, water doesn’t just pool—it migrates. I’ve pulled up tiles to find joists with soft rot, insulation saturated like a sponge, even active Stachybotrys growing behind the membrane. And the worst part? The damage is silent. You won’t hear it. You’ll just smell it… eventually.
Replacing the flange isn’t glamorous. It’s messy, precise, and demands respect for the layers beneath your feet. But do it right, and you stop the rot before it starts. Do it wrong, and you’re signing up for a £2,500 remediation job. Let’s get it right.
With over 14 years as a certified wet-room installer and Level 3 NVQ in Plumbing & Domestic Heating, I’ve replaced or repaired over 700 shower drain assemblies. My focus has always been on long-term waterproofing integrity, not just quick fixes. I’m NICEIC-registered for integrated electrical plumbing systems and routinely consult on bathroom renovations where drainage failure has compromised safety. One job in Croydon still sticks with me—a luxury walk-in shower installed just two years prior, already leaking beneath the floor. The contractor had used a cheap PVC flange from a DIY chain, torqued the screws like they were holding a car engine together. The flange warped, the seal failed, and the homeowner discovered black mould behind their bathroom wall during a redecoration. Total repair cost: £3,800. That’s why I preach flange quality and proper installation. It’s not just plumbing. It’s structural hygiene.
Quick Steps:
1. Remove shower grate and inspect flange for cracks, warping, or movement
2. Cut away grout and carefully extract old flange from drain pipe
3. Clean and deburr the drain pipe, ensuring a smooth surface
4. Dry-fit the new flange, mark alignment, then remove
5. Apply PVC cement to pipe and flange socket, insert with correct orientation
6. Reinforce with stainless steel screws into the subfloor
7. Seal underside with waterproofing membrane compatible with your system
Understanding the Shower Drain Flange
The shower drain flange is the metal or plastic ring you see when you lift the shower grate. But that visible part is just the tip. Beneath it, the flange extends down into the drain pipe—typically 40mm or 50mm PVC—and is bonded to create a watertight seal. It also has a flat base that sits flush against the subfloor, allowing your waterproofing membrane (like Schlüter Kerdi or Laticrete Hydro Barrier) to wrap seamlessly over it. This is critical. If the flange isn’t level, sealed, and stable, water finds a path under the tile, leading to rot, odours, and eventual floor collapse.
There are two main types: PVC and brass. PVC flanges, like the McAlpine 40101, cost £18.99 at Screwfix (2025 pricing) and are fine for standard installations. But I prefer brass flanges—specifically the Oatey Sure-Set Brass Drain Flange (Model 39070)—because they’re dimensionally stable, resist warping from heat, and thread perfectly with stainless steel screws. They cost more—£42 at Plumb Center—but last decades. I once removed a 1987 brass flange from a Manchester flat that still had perfect threads. The PVC one next to it? Crumbled in my hand.
Some flanges come with integrated weep holes—tiny channels that allow water trapped under the tile to drain into the main pipe instead of pooling. These are essential in wet rooms. The Schlüter RENO-DIL 50mm flange includes this feature and costs £65, but it’s worth it for peace of mind. Avoid universal flanges that claim to fit “any pipe.” They rely on rubber gaskets that compress unevenly and fail within 3–5 years. I’ve seen it too often.
Tools and Materials You’ll Need
Skip the guesswork. Here’s exactly what I use on every flange replacement job:
- Oatey 39070 Brass Drain Flange – £42, Plumb Center (2025)
- 40mm to 50mm PVC Pipe Deburring Tool – £15, B&Q
- Oatey PVC Cement (Solvent Weld) – £12, 250ml tin
- Stainless Steel Wood Screws (No. 8 x 1.5”) – 4 pcs – £4, Wickes
- Angle Grinder with Masonry Blade – for cutting grout (I use Bosch GWS 7-125)
- Hacksaw or PVC Pipe Cutter – for trimming pipe if needed
- Torpedo Level – to check flange alignment
- Caulking Gun and Silicone Sealant (non-acidic) – for final sealing
- Shop Vac – because dust and debris will fly
Optional but recommended: a flange alignment tool. The Oatey model keeps the flange perfectly centred during curing. Costs £28, but saves time and prevents rework.
One pro tip: use blue masking tape to mark your screw positions on the subfloor before applying cement. Once the flange is in, you can’t see the wood. I learned this the hard way on a job in Leeds—drilled one screw into thin air, missed the joist entirely. Had to patch and re-drill.
And don’t skimp on ventilation. PVC cement emits fumes that’ll give you a headache in minutes. Open windows, use a fan, or wear a respirator with organic vapour cartridges. I keep a 3M 6800 half-face mask in my van for jobs like this.
Step 1: Remove the Old Flange
Start by removing the shower drain grate. Most twist off or are held by two screws. If it’s stuck, don’t force it—wrap pliers in a cloth and gently loosen. Once removed, inspect the flange. Wiggle it. If it moves, it’s done.
Next, cut the grout around the flange using an angle grinder with a masonry blade. Be precise. You only need to remove 10–15mm of grout to free the flange from the tile bond. I use a depth gauge on my grinder set to 12mm to avoid slicing into the membrane below.
Now, the tricky part: separating the flange from the drain pipe. If it’s PVC, it was likely solvent-welded. You’ll need to cut it off. Use a hacksaw blade or a compact oscillating tool (I prefer the Fein MultiMaster) to make two vertical cuts on opposite sides of the flange collar. Don’t cut into the pipe—just deep enough to split the socket. Then, pry it apart with a flathead screwdriver.
If it’s a brass flange, it might be threaded or compression-fitted. Try unscrewing it first with a pipe wrench. If seized, you’ll need to cut it. Same method—two vertical cuts, then collapse and remove.
Once the flange is out, inspect the drain pipe. It should be clean, round, and free of cracks. If it’s damaged, you’ll need to cut it back and install a repair coupling. More on that in our step-by-step installation guide.
Step 2: Prepare the Pipe and Subfloor
This is where most DIYers rush and regret it. A sloppy prep means a failed seal.
First, deburr the inside and outside of the drain pipe. Use a 40–50mm deburring tool to remove any ridges or burrs left from cutting. A rough edge prevents a full solvent bond and can nick the O-ring on compression flanges.
Next, dry-fit the new flange. Push it onto the pipe without cement. It should slide on about 25–30mm. If it’s too tight, re-deburr. If too loose, the pipe may be damaged—replace it.
Check the flange height. It must sit flush or slightly below the finished tile surface—ideally 1–2mm lower. If it sticks up, your tile won’t sit flat. If it’s too low, water pools. Use a torpedo level across the top to ensure it’s perfectly level. I’ve seen flanges tilted 5 degrees, creating a permanent puddle in one corner of the shower.
Now, mark your screw holes. Rotate the flange so the weep holes (if present) face the drain outlet. Tape the flange in place, then drill pilot holes through the mounting tabs into the subfloor. Use 1/8” drill bit for No. 8 screws. Make sure you’re hitting solid wood—not just chipboard or plywood. I once drilled into a void and had to epoxy-anchor the screw. Not ideal.
Remove the flange. Time to bond.
Step 3: Install the New Flange
Apply PVC cement evenly to the inside of the flange socket and the outside of the drain pipe. Don’t skimp—this is a solvent weld, not glue. The cement softens both surfaces, fusing them into one solid piece.
Push the flange onto the pipe with a quarter-turn twist to spread the cement. Hold it in place for 30 seconds. Don’t adjust it—once it’s on, it’s on. The bond sets fast.
Now, drive your stainless steel screws through the mounting tabs into the subfloor. Torque them evenly—don’t overtighten. Brass is strong but brittle. I use a hand screwdriver for the last few turns to feel resistance. Snug, not strained.
If you’re using a flange with weep holes, ensure they align with the drain body’s channel. Misalignment traps water. The Schlüter system includes a small alignment key—use it.
Finally, seal the underside. Run a bead of non-acidic silicone around the base of the flange where it meets the subfloor. This isn’t structural—it’s a secondary barrier against lateral moisture migration. I use Everbuild 505 Clear Silicone, £6.50 a tube. Let it cure 24 hours before proceeding.
Step 4: Reconnect the Waterproofing and Tile
This step is often overlooked but is critical for long-term performance.
If you’re using a bonded waterproofing membrane (like Kerdi or Wedi), now’s the time to integrate it. Cut an X in the membrane and pull it up over the flange base. Use Kerdi-Fix or equivalent to seal the overlap. The membrane must make full contact with the flange’s sealing surface—no gaps.
For liquid membranes (Laticrete Hydro Ban, BAL Quad, Mapei Aquadefense), apply two full coats, extending at least 150mm beyond the flange. Let cure per manufacturer specs—usually 24–48 hours.
For detailed material comparisons and brand-specific tips, check our product recommendations. Need a full walkthrough from tear-out to tile? Our step-by-step installation guide covers every phase with photos and diagrams. Always verify compatibility between your flange and waterproofing system—see the product recommendations section for tested pairings.