Why Does My Shower Turn Cold After 5 Minutes?

Start by answering two questions: is it only the shower, and what kind of water heater do you have?

Graphic: summary of this guide, made by our team from the cited sources.

First, narrow it down

What you notice	Most likely area
Shower goes cold, kitchen and bathroom taps stay hot	The shower valve, not the heater
Every tap runs out of hot water fast	The water heater
Started suddenly on an electric tank	Lower element or its thermostat
New heater gives less hot water than the old one	Lower factory temperature setting or shorter dip tube
Only when the dishwasher, laundry or another shower is running	Demand larger than the heater can supply
Tankless: hot, then cold, then hot again	Flow dropping below the activation rate
Gas tank: no hot water at all after it ran out	Pilot or burner issue; call a pro

Is your tank big enough for how you use it?

Water heaters are sized by first hour rating (FHR), the gallons of hot water a full tank can deliver in an hour. The Building America Solution Center explains that the FHR should match your household's peak-hour demand (BASC). AHRI's worksheet counts 20 gallons of hot water for each shower, 14 for a dishwasher and 32 for an automatic clothes washer (AHRI).

So two showers plus a dishwasher run in the same hour is about 54 gallons of demand by that worksheet. If your heater's FHR, listed in its manual or specifications, is lower than your real peak hour, cold showers at busy times are expected, not a fault. Spreading out showers, laundry and the dishwasher is the free fix.

If the shower goes cold after five minutes even when nobody else is using hot water, keep going.

Electric tank: test the lower element and dip tube

A. O. Smith notes that newer heaters ship with lower factory temperature settings and shorter inlet (dip) tubes, both of which reduce how much hot water you get (A. O. Smith Bulletin 36). Its test for a heater that is not giving enough hot water:

1. Time how long it takes to fill a 1-gallon bucket at the faucet nearest the heater. Flow in gallons per minute is 60 divided by the seconds it took.
2. With power off at the breaker, set both upper and lower thermostats to 130°F, close the covers and restore power. (A. O. Smith suggests a service person if you are not comfortable with any step.)
3. Run about 15 gallons of hot water, shut it off, and give the heater about 45 minutes to recover.
4. Measure the hot water temperature at a nearby faucet with a candy thermometer. It should be 120°F to 140°F.
5. Keep running hot water until about 60% of the tank's capacity is used (for example 24 gallons from a 40-gallon tank, 30 from a 50-gallon tank), then measure again.
6. The temperature should have dropped only about 30°F.

What the results mean, per A. O. Smith: if the first reading was out of range, check the thermostats. If you lost more than 30°F by the end, check the lower element and the dip tube (A. O. Smith Bulletin 36).

Why the lower element matters: on a typical two-element heater, the upper element heats the top of the tank and the lower element heats the rest. If the lower one fails, you get a small amount of hot water from the top and then it runs cold, which is exactly the five-minute pattern.

Safety: electric water heaters run on 240 volts. Testing elements for continuity means opening covers near live terminals. Turn the breaker off and confirm the power is off, or have a licensed plumber or electrician do it. If the heater is also tripping its breaker, see our guide on why a water heater keeps tripping the breaker.

Gas or electric tank: the dip tube

Cold water enters a tank heater through a long plastic dip tube that carries it to the bottom. If the tube is cracked, missing or too short, incoming cold water mixes into the hot water at the top, and the shower cools quickly. A. O. Smith lists a "cracked, missing, or short dip tube" as a cause of not enough hot water in both its gas and electric bulletins, and has a separate bulletin on crumbling dip tubes (A. O. Smith technical bulletins).

Dip tube replacement involves shutting off water and power or gas and draining part of the tank. It is a reasonable pro job.

Tankless: the burner may be shutting off

Tankless heaters only fire when water flows above a minimum rate. Bosch's service bulletin for its gas tankless models gives an activation rate of about 0.5 gallons per minute at the lowest setting and about 1 gallon per minute at the highest, and says the burners go out if flow drops below it (Bosch). Other brands differ, so check your manual for the number.

Bosch's checklist for water going cold mid-use:

• Clean or replace the filter screen in the heater's water inlet.
• Remove and clean faucet aerators and showerheads; soak mineral deposits in vinegar.
• A hand-held shower hose may be too restrictive; a larger-diameter hose or a fixed head can raise flow.
• Clean or replace a whole-house filter if you have one.
• Do not add so much cold water at the shower valve that total hot flow falls below the activation rate. Bosch notes this happens most in late summer, when incoming water is warm.
• On a private well, keep pressure steady; Bosch lists a minimum of 30 psi during operation.

Only the shower? Check for a crossover or the shower valve

If sinks stay hot but the shower does not, the problem is probably at the shower valve. Bosch describes a crossover test: turn off the cold water supply to the water heater only, open each hot tap to hot only, and wait 5 minutes. Any water still flowing, even a trickle, means cold water is crossing into the hot side somewhere, or the scald protection in a shower valve is misadjusted (Bosch). Bosch's advice is to consult a plumber or the faucet valve maker for the repair.

Single-handle shower valves often have an adjustable limit that sets how far the handle can turn toward hot. If someone set it low, the shower never gets as hot as the taps. The valve maker's instructions show how to adjust it.

When to call a plumber

• Element, thermostat or dip tube replacement on a tank heater, unless you are comfortable working with 240-volt power or gas.
• A gas heater whose pilot or burner keeps going out, or any smell of gas. Leave the house and call the gas utility from outside.
• The crossover test shows flow on the hot side.
• The tank is too small for your household and you are weighing a replacement.