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Hot water runs out, or swings hot and cold?

Showers that turn cold, hot water that takes forever, or none at all. The cause depends on whether you have your own heater or a building system.

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Takes about a minute. Tell us what's happening, what kind of building it is, and the town or neighborhood.

Check this first
  1. Apartment building? Ask neighbors; if they have the same problem, it's the central system. Tell the super or management.
  2. Own water heater? Look for water around the tank and check that the gas pilot or electric breaker is on.
  3. Water heater leaking from the bottom? Close the cold-water inlet valve, turn the heater off, and call.
  4. Smell gas? Leave and call 911 or the gas utility from outside.

01In short

In houses and two-family homes, hot water usually comes from a tank water heater or a boiler coil, and problems are usually sediment, a failed part or an undersized heater. In apartment buildings, a central system feeds everyone; temperature swings often come from old shower valves or a mixing valve, and outages are a building issue.

Typical gas water heater connectionsDiagram D5
  • Cold water
  • Hot water
Typical gas tank water heater connections A tank water heater with a cold-water inlet and shutoff valve, a thermal expansion tank on the cold side where required, a hot-water outlet, a temperature and pressure relief valve with a discharge pipe ending near the floor, a drain valve at the bottom, and a gas supply with a shutoff valve and sediment trap. The flue vent rises from the top. Requirements vary by code and model. flue vent expansion tank T&P relief valvedischarge pipe ends near floor drain valve gas supply + shutoffsediment trap 123456
  1. 1Cold-water inlet with shutoff valve
  2. 2Thermal expansion tank (where required, e.g. with a check valve or pressure regulator)
  3. 3Hot-water outlet to fixtures
  4. 4Temperature & pressure (T&P) relief valve and discharge pipe: never cap or plug it
  5. 5Drain valve for flushing sediment
  6. 6Gas supply with shutoff and sediment trap: gas work is for licensed professionals only

Simplified, not to scale.

02Common signs

  • Hot water runs out quickly
  • Shower turns hot or cold when someone flushes or runs water
  • Long wait for hot water at the tap
  • Lukewarm water only
  • Rusty hot water or popping noises from the tank

03Possible causes

Common causes
SymptomOwn water heaterApartment building
Runs out fastSediment, failed lower element, dip tube, undersized heaterCentral heater capacity, recirculation problem
Temperature swingsOld shower valve without pressure balancingOld shower valve; building mixing valve
Long waitLong pipe run from the heaterRecirculation pump off or failing
No hot waterPilot, igniter, thermocouple, element, breakerCentral boiler or heater outage
Rusty water, noisesAging tank, sedimentAging system or piping

04What you can safely check

  • Whether neighbors are affected
  • The water heater's age (often printed on the label) and any leaks
  • Whether the problem is one fixture or all of them
Don't
  • Relight a gas pilot repeatedly if it keeps going out
  • Cap or plug the relief valve pipe
  • Open an electric heater's panels with power on

05When to call a plumber

  • No hot water and the cause isn't obvious
  • The tank leaks
  • The relief valve drips
  • Temperature swings at a shower: the valve needs replacing

A plumber checks controls, venting, the relief valve and sediment, and replaces parts or the heater; for showers, a pressure-balancing valve stops swings. See water heaters.

06By building type

Rentals & co-ops
Usually central hot water: report to management.
Condos
Some have in-unit heaters; others are central.
Houses & two-families
Own tank heater or boiler coil, often one per unit.

07Local considerations

Renting in NYC? Building owners are generally responsible for plumbing repairs in rental apartments. Tell the super or managing agent; if repairs aren't made, you can contact 311. In co-ops and condos, the proprietary lease or declaration decides who fixes what.

08Frequently asked questions

How long do water heaters last?

It varies with water quality, use and maintenance. Signs it's time: leaks from the tank, rusty hot water and frequent repairs.

Why does my shower get hot when someone flushes?

Older valves don't compensate when cold-water pressure drops. A pressure-balancing or thermostatic valve fixes it.

Sources & review

Last reviewed . General information, not legal or engineering advice. Rules change and individual buildings differ.

  1. NYC Department of Buildings, Plumbing Permits
  2. NYC Rent Guidelines Board, 2023 Housing Supply Report (NYC HVS 2023)

How it works

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