No Cold Water at One Fixture Diagnostic Decision Tree

Why this matters

A homeowner reports "no cold water at the kitchen sink" but hot is fine, or vice versa. The call sounds simple and ends up as a 90 minute diagnostic tour through stops, cartridges, supply lines, and pressure tests because two single-handle mixer faucets and three thermostatic showers share the same failure modes for completely different reasons. This decision tree isolates the failure to the fixture, the stop, or the supply line in under 15 minutes without cutting drywall.

Frame the call before turning a wrench

Before opening the cabinet:

1. Confirm which fixture is reporting the problem; ask the homeowner to demonstrate
2. Test the adjacent fixtures on the same supply branch. If the powder room next to the kitchen sink also has no cold water, the problem is upstream of both fixtures
3. Test both hot and cold at the affected fixture independently using the handle full deflection in each direction
4. Note the failure mode precisely: no flow, low flow, slow to start, intermittent, sputtering air, hot water comes from cold handle, or rust-colored water

The wrong characterization of the failure mode sends the truck for the wrong parts.

Branch 1: Single-handle faucet, no cold flow

Most single-handle faucets blend hot and cold through a cartridge or a ceramic disc valve. Symptoms:

• Hot side delivers normal flow when handle is at hot stop
• Cold side delivers nothing or trickle when handle is at cold stop

Likely causes in field-call order:

1. Cold supply stop closed under cabinet (50 percent of these calls)
2. Cold supply line kinked or restricted (braided stainless flex with internal liner failure is common)
3. Faucet cartridge debris on the cold inlet port. Pull the cartridge, inspect the inlet ports, flush
4. Frozen cold supply line (winter calls in unheated cabinet)
5. Sediment accumulation in the angle stop (older 1/4 turn stops fail open or partially closed)

Verification: close both stops, disconnect both flex lines at the faucet, place buckets, open the cold stop only. If cold stop flows full volume into the bucket, the problem is downstream (flex line or faucet). If cold stop barely flows, the problem is upstream (stop or supply branch).

Branch 2: Two-handle faucet, no cold flow

The cold handle is mechanical and directly controls a stem cartridge or compression valve. Same supply isolation as Branch 1 plus:

• Stem cartridge stripped or worn (compression seat washer destroyed but the stem still turns)
• Cartridge installed upside down (during a prior repair) with cold port now blocked
• For ceramic disc cartridges (Delta, Moen, Price Pfister), the disc spring may have failed

Verification: remove the cold handle and stem. Open and close the supply stop with the stem out. Water should flow from the open stem hole at full pressure with the stop open. Reinstall the stem in original orientation.

Branch 3: Pressure-balanced shower valve, no cold flow

Symptoms:

• Shower runs hot only
• Cold side from the same valve to the tub spout also fails
• Adjacent hot or cold fixtures elsewhere in the house may or may not work

Likely causes:

1. Pressure-balance spool (the brass piston inside Moen Posi-Temp, Delta Multi-Choice, Symmons Temptrol) stuck in the hot position. The spool is supposed to throttle hot if cold pressure drops; when stuck, you get all hot. Replace the spool or the cartridge depending on the valve brand.
2. Shower volume control cartridge worn
3. Cold inlet integral check stop closed (most modern pressure-balance valves have integral hot and cold stops; verify both open)
4. Anti-scald limit ring mis-set during prior service (also rejects cold)

Verification: shut both house mains, then open only the cold main. The pressure-balance spool should center; if water still does not flow from the showerhead with cold-only available, the cartridge is the suspect.

Branch 4: Thermostatic shower valve, no cold flow

Thermostatic valves (Grohtherm, Kohler, Hansgrohe ShowerSelect, Symmons Tempress) blend internally based on a wax-element thermostat. Symptoms identical to pressure-balance valves.

Likely causes:

1. Thermostatic element seized at high temperature; the unit blends all hot to maintain setpoint
2. Cold inlet stop closed (often a screwdriver-slot stop integrated into the rough-in valve body, easy to miss)
3. Scale buildup on the element shuttle (water hardness over 7 grains per gallon dramatically shortens thermostatic cartridge life)

Verification: remove the temperature handle, expose the cartridge stem. Use a manufacturer-specific scale removal kit (vinegar soak for most brands) or replace the cartridge.

Branch 5: Only the cold side fails, all fixtures in the house

This is no longer a single-fixture call. Suspect:

1. Main shutoff valve partially closed at the meter or PRV
2. Pressure-reducing valve (PRV) failed; install a gauge to verify static pressure at a hose bibb
3. Whole-house water filter cartridge clogged (very common cause when a single homeowner replaced the cartridge with a higher-MERV equivalent)
4. Frozen cold main between the meter and the house in winter
5. Galvanized pipe corrosion narrowing the cold branch (older homes pre-1965)

Verification: open hot at one fixture, cold at another, watch flow at each. If hot delivers normal but cold delivers nothing house-wide, the cold-only branch is the suspect.

Branch 6: Air sputters from the cold side

Air on the cold side typically means a supply break or a recent supply shutoff that pulled air into the line.

Likely causes:

1. Burst pipe in a wall cavity (water present elsewhere in the home)
2. Recent main shutoff with air introduced
3. Well pump system: bladder tank waterlogged or pump priming
4. Backflow event (rare but check vacuum breakers at outdoor sillcocks)

Verification: open every fixture cold side fully for 60 seconds to bleed air. If air does not clear, escalate to whole-house diagnostic.

References

• International Plumbing Code (IPC) 2024 Chapter 6 Water Supply and Distribution
• ASME A112.18.1 / CSA B125.1 Plumbing Supply Fittings
• ASSE Standard 1016-2017 Performance Requirements for Automatic Compensating Valves (anti-scald)
• NFPA 51B Standard for Fire Prevention During Welding, Cutting, and Other Hot Work