Hot water running out fast or going cold mid-shower? Learn the five common causes, from sediment to a broken dip tube, and which need replacement.
If your shower used to last fifteen minutes and now goes cold in five, something changed. Water heaters do not gradually get smaller, so there is a specific cause. Here are the five, roughly in order of how often we find them.
The most common cause in Arizona, and the one people never guess. Hard water deposits minerals in the bottom of the tank. That layer is not just insulating the burner - it is physically occupying space that used to hold hot water.
A 50-gallon heater with several inches of sediment might be storing 35 gallons of usable hot water. You have not changed your habits; the tank has shrunk.
Fix: a flush, as part of water heater repair & replacement. On a heavily scaled older tank this helps less than people hope, but on a mid-life unit it can restore most of the capacity.
The dip tube carries incoming cold water down to the bottom of the tank so it heats from below and the hot water at the top stays undisturbed. When the tube cracks or breaks off near the top, cold water enters at the top and mixes straight into the hot layer you are drawing from.
The signature: water that is lukewarm rather than hot from the start, and a very sudden reduction in how long it lasts. It is a cheap part and a good outcome when this turns out to be the cause.
On an electric heater there are two elements. If the lower one fails, only the top of the tank heats, so you get a short burst of hot water and then cold. This is such a distinctive symptom that it is often diagnosable on the phone.
On a gas unit, a failing thermostat or a burner struggling through scale produces slow recovery - the tank does eventually reheat, just far too slowly to be useful.
Nothing has failed; demand changed. A teenager moved in, someone fitted a rain shower head, a bathroom was added. A 40-gallon tank that served two people does not serve four.
Options: a larger tank, or tankless water heater installation, which removes the capacity question entirely. Tankless makes most sense if you are running out regularly, want the floor space back, or plan to stay in the house long enough to earn back the install cost.
If heated water is escaping before it reaches the shower, you will run out faster and your gas or electricity bill will climb at the same time. In Arizona, a slab leak on the hot side is a genuine contender - and a warm patch on the floor is the giveaway. That is slab leak detection & repair.
No warm floor but a rising bill? Turn everything off and watch the meter. If it moves, leak detection & water leak repair is the next step.
Before you call, check the thermostat. 120°F is the standard setting. If someone turned it down, or if a mixing valve has drifted, you get exactly this symptom for free. Worth ten seconds of your time.
Rough guide:
Everything above traces back to scale. An annual flush, an anode rod checked every couple of years, and - the one that changes the maths most - a water softener & water treatment installation so the sediment stops arriving in the first place.
Call and describe what you are seeing. We will tell you whether it is a tonight problem or a Tuesday problem.