Shower and tub plumbing, including the leak behind the tile

Dripping shower valves

A shower that drips after being turned off is a worn valve cartridge in the great majority of cases. The seal inside the cartridge no longer closes fully, and the drip continues until the pressure behind it equalises, or indefinitely.

It matters more than a dripping sink tap for two reasons. First, the drip usually falls onto tile or a pan and the water goes down the drain unseen, so it runs for months without anyone treating it as urgent. Second, a valve that is failing internally may also be failing at its body seals, and that water goes into the wall rather than down the drain.

Repair is usually a cartridge replacement, done through the trim plate without disturbing tile. The challenge is identification: shower valve cartridges are highly model-specific, and a valve installed thirty years ago may need a part that is no longer made. Where the cartridge is obsolete, the choice is a rebuild kit if one exists, or valve replacement, which does involve access.

A drip that started suddenly across several fixtures at once, shower, taps, toilet fill valves, points at system pressure rather than wear. Worth checking a gauge reading before replacing parts repeatedly.

Temperature that will not hold

Showers that run hot then cold, or that surge when a toilet is flushed, are one of the most common complaints and there are several distinct causes.

A failing pressure-balancing cartridge. Most modern shower valves balance hot and cold pressure so that a drop on one side reduces the other proportionally, protecting you from a scald when someone flushes. When the balancing spool sticks, the protection stops working and temperature swings return.

No thermostatic or balancing valve at all. Older two-handle and simple mixing valves offer no protection whatsoever. Massachusetts code has long required anti-scald protection on new work, and retrofitting it to an old shower is a genuine safety improvement, particularly with children or older adults in the house.

Undersized or shared distribution. If the shower goes cold whenever another fixture draws, the pipework cannot supply both at once. That is a flow problem: see water pressure problems.

Water heater issues. Running out of hot water mid-shower is capacity or recovery, not the valve. On a tankless unit, temperature instability often traces to gas supply or scale: see tankless water heaters.

A failed mixing valve at the heater, which can bleed cold into the hot supply and produce lukewarm water everywhere.

Weak or uneven spray

Nearly always scale. Shower heads have dozens of small outlets and in hard-water areas they mineralise up until the spray is patchy and weak. Removing the head and soaking it in descaler restores it completely, and rubbing the nozzles with a thumb clears the softened deposit. It is a ten-minute job with an immediate result.

If cleaning does not fix it, check the flow restrictor inside the head, which can clog with grit, particularly after any work on the mains that has disturbed debris into the system. Then check the valve cartridge, which can partially block for the same reason.

Where the whole bathroom is weak rather than just the shower, look upstream: isolation valves, distribution pipe size, or corroded supply piping. And where the problem is only hot, look at the water heater.

One thing worth mentioning: some very old shower arms and drop-ear elbows are galvanised and internally corroded to a fraction of their bore. No amount of cleaning the head fixes that, and the arm needs replacing.

Slow shower and tub drains

Hair, and further down the pipe than most people expect. A tub or shower drain that has slowed gradually over a year or two is almost always accumulating hair bound with soap residue in the trap and the first few feet beyond it.

What works: removing the strainer or the tub's overflow plate and pulling the debris out mechanically. A hand auger fed gently down the drain clears most of what remains. What does not work well is chemical drain cleaner, which struggles with a hair mass and damages older pipe.

Tub drains have an additional complication in the trip-lever or pop-up linkage inside the overflow tube, which collects debris and can also fall out of adjustment so the stopper never lifts fully. Adjusting that linkage sometimes solves what looks like a blockage.

If the shower drains slowly and other fixtures gurgle, or waste appears when another fixture is used, the problem is downstream and shared. That is a drain or vent issue rather than a hair clog: see drain cleaning.

Standing water in a shower with no obvious blockage occasionally points at a pan that has settled or was never pitched properly to the drain, which is a construction defect rather than a plumbing one.

Leaks into the ceiling below

This is the section that matters. A shower leaking into the structure is usually discovered as a stain on the ceiling underneath, by which point the leak has been running for a while.

The candidates, and they are diagnosed differently:

• The valve body or its connections inside the wall, water appears whenever the shower runs, and often shows as a stain on the wall below the valve rather than under the pan.
• The drain connection at the pan or tub, water appears when the shower runs and drains, and typically shows directly beneath the drain.
• Failed pan or membrane, where the waterproofing under the tile has failed. Water travels along framing and can surface some distance from the shower.
• Failed grout, caulk or tile letting water into the wall assembly at the corners or where the pan meets the wall, the most common cause in older tiled showers.
• The tub overflow gasket, which leaks only when the bath is filled above the overflow.
• Supply pipework in the wall, unrelated to the shower's use.

Narrowing it down is largely a matter of controlled testing: running the shower without the drain flowing, filling and draining the tub, running only the overflow, and watching where and when water appears. Where that is inconclusive, thermal imaging and moisture mapping locate it without opening the wall on a guess: see leak detection.

Replacing a valve behind tile

The question everyone asks is whether the tile has to come off, and the honest answer is: sometimes, but less often than you might expect.

Where the same manufacturer's replacement valve fits the existing rough-in, the work can often be done through the existing trim opening. Where the valve is obsolete or a different type is being fitted, access is needed, and the best option is usually from behind, through the wall of an adjacent closet, bedroom or hallway, leaving the tiled face untouched. That is a drywall repair on a non-tiled wall rather than a tiling job, and it is a very large saving.

Where neither is possible, tile has to be removed. A careful plumber removes the minimum, and it is worth knowing in advance whether you have spare matching tile, because for anything more than a few years old you almost certainly cannot buy a match.

Ask specifically at quote stage: where will access be taken from, how large an opening, and who closes it. An access panel fitted in an inconspicuous location is often the sensible long-term answer, since a valve replaced once will need attention again eventually.

Tub and shower replacement

Replacing a tub or shower is a bigger project than it looks, because the plumbing, the waterproofing and the finishes are all interdependent.

Key points that get missed. The drain position is fixed by the existing waste pipe, and a new unit with the drain in a different place means opening the floor. Pan pitch and waterproofing are what stop the next leak, and skimping there is why so many tiled showers fail after ten years. Valve rough-in depth must suit the new wall build-up, or the trim will not sit correctly. Venting must be adequate for the new arrangement. And converting a tub to a walk-in shower changes the drainage and often needs the waste re-piped.

Accessibility work is worth planning properly rather than adapting later: a curbless entry, a correctly located mixing valve reachable from outside the spray, grab bar blocking installed in the framing while the wall is open, and a handheld on a slide bar. Doing that at the point of replacement costs a fraction of retrofitting it.

For a whole-bathroom project, see bathroom remodel plumbing.