Hot water runs out too fast

Q: Hot water runs out too fast

In Canada, when a gas water heater runs out of hot water too quickly, the most common causes to rule out are a thermostat dial set too low, more demand than the tank size can keep up with, and sediment that has quietly stolen capacity over the years. A broken dip tube can also send cold water straight to the top so it mixes out fast. If it always drained fast from day one, the tank is likely undersized for the household. Raise the dial only toward about 49C/120F — no higher, because scalding is a real risk with kids or older adults. Persistent trouble with only part of the tank heating can point to a failed burner or gas control, which is licensed work. If the water comes out scalding or steaming, or you smell gas, stop and call a plumber or your gas utility.

Short showers are a nuisance, but the cause is usually mundane — a low dial, a tank that's simply too small for a busy morning, or years of sediment stealing capacity. Most fixes are cheap or free.

tuneWhat are you noticing?

Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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In Canada, if the tank has always run out fast from day one, size is the likely answer, not a fault. Count the back-to-back demands — long showers, a soaker tub, laundry and dishes at once. Ruling this in costs nothing: stagger usage and see if the problem disappears. A larger tank or a tankless upgrade is the longer-term fix.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

handymanHow to fix it

warning The water and tank are scalding during a flushYou'll be draining tank-hot water — hot enough to burn. Let the tank cool for an hour or two first, wear closed shoes, keep the hose routed to a drain so no one is splashed, and keep children and pets clear of the work area. If the drain valve is corroded or won't reseal afterward, stop and call a plumber rather than forcing it.

Turn the gas control to pilot, shut the cold-water inlet, connect a hose to the drain valve, and drain-and-flush the tank until the water runs clear before refilling and relighting.

Set the gas control to "pilot" so the burner won't fire on an empty tank, and close the cold-water shutoff above the heater.
Connect a garden hose to the drain valve at the base and run it to a floor drain or outside. Open a hot tap upstairs to break the vacuum.
Open the drain valve and let the tank empty. Once low, briefly reopen the cold inlet in bursts to stir and flush sediment until the draining water runs clear.
Close the drain, refill fully (hot tap runs steady with no sputter), then return the gas control to its normal setting and confirm the burner lights.

schedule60 min savingsusually free

handymanHow to fix it

report Never set the tank above about 49C/120FTurning the dial higher gets you a little more hot water at a real cost: at 60C/140F a child or older adult can suffer a third-degree burn in seconds; at about 49C/120F it takes minutes. Cap the setting at roughly 49C/120F. If you need more hot water than that provides, the answer is a bigger tank or a tankless unit, not a hotter one — not a higher dial.

Open the access panel, turn the gas control dial up gradually toward about 49C/120F — no higher — wait an hour, and measure the water at a tap with a thermometer before deciding it's enough.

Find the temperature dial on the gas control valve at the front of the tank. Many dials are marked with reference points rather than degrees.
Turn it up a small amount at a time toward the "hot" reference (about 49C/120F). Do not go past it.
Wait about an hour, then run a hot tap and hold a thermometer under the stream. If it reads near 49C/120F and showers last longer, you're done; if not, move on to sizing, sediment, or the dip tube.

schedule15 min savingsusually free

visibilityHow to check

Run a hot tap and time how the temperature falls. Water that drops from hot to merely warm within a minute or two — rather than staying hot then going cold — points to cold water mixing in at the top.
Unscrew a faucet aerator or two and look for small white or bluish plastic flakes. A dip tube that's cracking often sheds bits that collect in aerators and screens.
Rule out the simpler causes first: confirm the dial isn't set low and that the shortfall isn't just heavy back-to-back demand. If it goes lukewarm fast with the dial up and light use, the dip tube is the prime suspect.

buildNo tools schedule15 min

handymanHow to fix it

warning Hot water, and don't force a corroded fittingLet the tank cool before draining so you're not working with scalding water. The cold-water inlet nipple can be seized on an older tank; steady effort is fine, but if it won't budge or the fitting looks corroded, stop and call a plumber rather than cracking a fitting on a full tank. This is a quick job for a pro if any of it feels beyond you.

Shut off the water and gas, drain the tank enough to work, disconnect the cold-water inlet nipple, pull the old dip tube, and drop in a matching replacement before reassembling and refilling.

Set the gas control to "pilot", close the cold-water shutoff, and drain a few litres from the tank so the water level is below the cold inlet.
Disconnect the cold-water line and remove the inlet nipple on top of the tank; the dip tube sits directly beneath it.
Lift out the old dip tube (note if it's cracked or crumbled) and insert a new one of matching length and material, seated fully into the fitting.
Reinstall the nipple and cold-water line, reopen the water, purge air at a hot tap, then return the gas control to normal and confirm the burner lights.

schedule75 min savings$15–40

Replacement water-heater dip tubeMatch the tank's inlet thread and the tube length; cross-linked polyethylene (PEX) tubes resist the cracking older plastic ones showed

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: licensed professionals only
Owner replacement of a dip tube is generally permitted as plumbing maintenance; any burner/gas-control work remains licensed gas work.

verifiedWhy this one goes to a pro

Diagnosing why only part of the tank heats means opening up the burner and gas control and working with live gas and a leak-tight reassembly. In every province this is work for a licensed plumber or gas-fitter — the risk of getting gas wrong is far greater than the cost of the call.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

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Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.