Water Heater Not Working?
Diagnose It Before You Call Anyone
Most water heater trouble comes down to a handful of parts, and the first fork in the road is fuel type: electric units fail at the heating elements and thermostats (cheap, often DIY-able), while gas units fail at the thermocouple, pilot, or gas valve (more caution warranted). The one symptom that almost always means replace rather than repair is water leaking from the tank body itself. Before you call anyone, figure out whether it's no heat, not enough heat, a leak, noise, or smell — that alone usually tells you whether it's a $20 part or a new heater.
The 9 Most Common Water Heater Problems
Each card below includes symptoms, the likely part, DIY difficulty, and a realistic cost if you hire a plumber. Open any card to see the full detail.
DIY — Moderate No hot water at all The single most common water heater complaint
Symptoms
- Water runs cold no matter how long you wait
- No hot water at any tap
- On gas units, the pilot may be out; on electric, a tripped breaker
Likely cause
On electric heaters, a failed upper heating element or thermostat, or a tripped high-limit reset, is the usual culprit. On gas heaters, it's typically a pilot that won't stay lit (thermocouple), a tripped thermal switch, or a failed gas control valve.
The part
Electric heating element or thermostat / Gas thermocouple
$10–$60
Home Depot/Lowe's or any hardware store; element ~$10-$25, thermostat ~$10-$20, thermocouple ~$10-$20
Difficulty
On an electric unit, swapping an element or thermostat is a real DIY job for a handy person, but it requires shutting off the breaker, draining the tank, and confirming power is OFF with a multimeter. On gas, relighting a pilot is easy; replacing a thermocouple is moderate; anything involving the gas valve is a pro job.
⏱ 1-2 hours
🔧 Multimeter (electric) · Element wrench or socket (electric) · Screwdriver · Garden hose to drain tank
ELECTRIC: 240V can kill — shut the breaker OFF and verify with a multimeter before touching elements. GAS: if you smell gas, leave and call the gas company; do not relight.
No hot water is usually a cheap part, not a dead heater. Electric folks: it's probably an element. Gas folks: probably the pilot/thermocouple. Don't let anyone sell you a whole new unit off this symptom alone.
DIY vs. Pro
First check the free stuff: breaker (electric) or whether the pilot is lit (gas). If power/pilot is fine, an electric element/thermostat swap is DIY-friendly; a gas-valve failure is a pro call. Never work on an electric element without confirming the breaker is off and testing with a meter.
If you hire a plumber
A plumber typically charges in the low-to-mid hundreds for an element or thermocouple replacement — well under the cost of a full water heater replacement, so this is worth repairing, not replacing.
DIY — Moderate Runs out of hot water too fast Among the top complaints, especially in growing households
Symptoms
- Hot water lasts only a few minutes
- Shower goes cold partway through
- Worse than it used to be
Likely cause
On electric units, a failed LOWER heating element is the classic cause — you get some hot water from the upper element but it runs out fast. Otherwise it's an undersized tank for the household, sediment reducing effective capacity, or a dip tube problem.
The part
Lower heating element (electric) or dip tube
$10–$30
Home Depot/Lowe's; lower element ~$10-$25, dip tube ~$10-$20
Difficulty
If it's a lower element on an electric unit, that's the same moderate DIY job as the upper element. If the tank is simply too small for your household, no repair fixes that — it's a sizing/replacement decision.
⏱ 1-2 hours
🔧 Multimeter · Element wrench/socket · Screwdriver · Garden hose
ELECTRIC: shut the breaker OFF and verify with a meter before touching the element.
If your hot water used to last and now doesn't, suspect the lower element before you blame the tank size. Cheap fix first.
DIY vs. Pro
Rule out a bad lower element (cheap, DIY) before concluding you need a bigger tank. If the element tests fine and the tank's just undersized for a grown family, that's a replacement/upsize conversation, not a repair.
If you hire a plumber
A lower-element replacement runs the same low-to-mid hundreds as the upper element. Upsizing to a larger tank is a full replacement job priced in the standard install range.
DIY — Easy Water not hot enough or too hot Common and usually the cheapest fix of all
Symptoms
- Water is lukewarm at best
- Or scalding hot and you didn't change anything
- Temperature drifted over time
Likely cause
A thermostat set wrong or failing. On electric units there are usually two thermostats; on gas it's the dial on the control valve. Sometimes it's literally just the setting.
The part
Thermostat (electric) or gas control dial
$0–$20
Free if it's just the setting; electric thermostat ~$10-$20 at any hardware store
Difficulty
Checking and adjusting the setting is free and easy. Replacing an electric thermostat is moderate (power off, meter, swap). The target is 120°F — higher wastes energy and risks scalding.
⏱ 5 minutes to adjust; ~1 hour to replace a thermostat
🔧 Screwdriver · Multimeter (only if replacing)
Set to 120°F: hotter than that risks scalding (especially kids/elderly); much lower invites bacteria growth.
Nine times out of ten this is a dial, not a defect. Set it to 120 and see — free is the best price there is.
DIY vs. Pro
Try the setting first — set it to 120°F. If it won't hold temperature after that, a thermostat may be failing, which is a moderate DIY job on electric or a pro call on gas.
If you hire a plumber
If it comes to replacing a thermostat, a plumber charges in the low hundreds. But often this costs you nothing but a minute at the dial.
Call a Pro Leaking from the tank itself Less common than the no-heat complaints, but the most consequential
Symptoms
- Water pooling under the center of the tank
- Rusty water around the base
- Leak that returns no matter what you tighten
Likely cause
Internal corrosion has perforated the steel tank. Once the tank body leaks, it cannot be repaired — the tank is done.
The part
None — the tank is not repairable
Free / no part needed
Difficulty
There is no DIY fix and no pro repair for a leaking tank body. The only answer is replacement. Your DIY role is damage control: shut off the water supply and the power/gas, and drain it to limit flooding.
⏱ N/A (replacement job)
🔧 Garden hose (to drain and limit damage)
FLOODING: shut the cold-water supply valve at the top of the heater. Then kill the power (breaker) or gas to avoid burning out elements/burner on an empty tank.
A weeping tank is a dead tank — no part fixes a rusted-through wall. But first make sure it's actually the tank and not a drippy valve up top, because that distinction is the difference between $150 and a new heater.
DIY vs. Pro
Don't let anyone talk you into 'repairing' a leaking tank — it can't be done. Confirm the leak is from the tank body (not a valve or fitting, which ARE repairable) before accepting a replacement quote.
If you hire a plumber
This is a full water heater replacement — see your metro's installed pricing. The repair-vs-replace math is settled here: it's replace.
DIY — Moderate Leaking from a valve or fitting Easy to confuse with a tank leak, but usually repairable
Symptoms
- Drip from the T&P (pressure-relief) valve or its discharge pipe
- Leak at the drain valve at the bottom
- Moisture at the cold/hot inlet or outlet connections on top
Likely cause
A failed or weeping temperature & pressure relief (T&P) valve, a drippy drain valve, or a loose/corroded supply connection. These are fittings on the tank, not the tank wall, so they can be fixed.
The part
T&P valve, drain valve, or supply connector
$15–$40
Home Depot/Lowe's; T&P valve ~$15-$30, drain valve ~$10-$20, flex connector ~$15
Difficulty
Tightening a fitting is easy. Replacing a T&P valve or drain valve is moderate — you shut off water and power/gas, relieve pressure, and swap the valve. A constantly weeping T&P valve can also signal excessive pressure or temperature, which is worth diagnosing, not just capping.
⏱ 30-90 minutes
🔧 Pipe wrench or channel-lock pliers · Thread tape · Garden hose
SCALDING/PRESSURE: a T&P valve is a safety device. Never cap or plug it to stop a drip — if it's releasing, there may be a real over-pressure or over-temperature problem.
Good news if the drip is from a valve or fitting up top — that's a cheap repair, not a new heater. Just never defeat the T&P valve; it's the thing standing between you and a tank that builds dangerous pressure.
DIY vs. Pro
A valve or fitting leak is genuinely repairable and often DIY for a handy person — a real cost saver versus assuming you need a new heater. But a T&P valve that keeps releasing may be doing its job (over-pressure/over-temp), so don't just plug it; find out why.
If you hire a plumber
A plumber typically charges in the low-to-mid hundreds to replace a T&P or drain valve — far cheaper than replacement.
DIY — Easy Popping, rumbling, or knocking noise Very common in older tanks and hard-water areas
Symptoms
- Popping or rumbling when the heater runs
- Crackling sounds
- Often paired with reduced hot-water capacity
Likely cause
Sediment (mineral scale) has built up on the tank bottom, trapping water beneath it that boils and percolates through the layer. Common in hard-water regions and aging tanks.
The part
None (it's a flush, not a part) — possibly a new anode rod
$0–$50
Free to flush; anode rod ~$20-$50 at Home Depot/Lowe's if you replace it while you're at it
Difficulty
Flushing the tank is a legitimately easy DIY maintenance job: hook a hose to the drain valve, drain and flush until clear. Doing it yearly prevents the buildup in the first place.
⏱ 30-60 minutes
🔧 Garden hose · Bucket
SCALDING: the drained water is hot. Let the tank cool or run the drained water somewhere safe.
Rumbling is your tank making popcorn out of sediment. Flushing it is a hose-and-a-bucket job you can absolutely do yourself — and doing it yearly is the cheapest way to make a heater last.
DIY vs. Pro
Flushing is easy and worth doing yourself. If a tank has years of hardened sediment, flushing may not fully clear it and the noise can persist — at that point it's a sign the tank is aging, not an emergency.
If you hire a plumber
A plumber will charge a service-call's worth (low hundreds) to flush a tank — which is why this is the classic 'just do it yourself' maintenance job.
DIY — Moderate Rusty or discolored hot water Common in older tanks; an early warning sign
Symptoms
- Brown, yellow, or reddish tint to hot water
- Metallic taste or smell
- Often hot side only (cold runs clear)
Likely cause
The sacrificial anode rod has been used up, so the tank's steel has started to corrode. If only the hot water is discolored, the heater (not your pipes) is the source.
The part
Anode rod
$20–$50
Home Depot/Lowe's or online; anode rod ~$20-$50
Difficulty
Replacing the anode rod is moderate DIY — it's a big hex head on top, but it's often torqued in tight and can require a breaker bar and some muscle. Catching it early (rusty water, before leaks) can add years to the tank.
⏱ 30-60 minutes
🔧 6-point socket / breaker bar · Garden hose · Thread tape
Rusty hot water is your anode rod waving a white flag. Swap it early and you can buy years; ignore it and you're shopping for a new heater sooner. Confirm it's the hot side only so you're not chasing a pipe problem.
DIY vs. Pro
If you catch rusty hot water early, a new anode rod is a cheap way to extend the tank's life — a worthwhile DIY for a confident person. If the tank is already old and the rust is heavy, you may be near replacement anyway.
If you hire a plumber
A plumber charges in the low-to-mid hundreds to replace an anode rod. Done early, it's far cheaper than a new heater down the line.
DIY — Moderate Smelly (rotten-egg) hot water Less common but distinctive and fixable
Symptoms
- Sulfur / rotten-egg smell from hot water
- Stronger on the hot side
- Often in homes on well water
Likely cause
Bacteria reacting with the anode rod produce hydrogen sulfide gas. It's a water-chemistry issue, not usually a tank failure.
The part
Aluminum/zinc or powered anode rod (and a tank sanitizing flush)
$20–$150
Home Depot/Lowe's for a standard anode (~$20-$50); a powered anode runs ~$80-$150 online
Difficulty
Same job as a regular anode swap (moderate), often combined with a sanitizing flush (hydrogen peroxide or a chlorine flush). Switching to an aluminum/zinc or powered anode usually solves recurring smell.
⏱ 1-2 hours including flush
🔧 6-point socket / breaker bar · Garden hose
Do NOT mix cleaning chemicals. If using a chlorine or peroxide flush, follow directions and ventilate.
Rotten-egg smell is bacteria meeting your anode rod, not a broken heater. A different anode and a sanitizing flush usually nails it — don't get talked into a whole-house system over a smell.
DIY vs. Pro
This is a DIY-friendly fix for a handy person and cheaper than any 'whole house' treatment a salesperson might push. If you're on well water and it keeps coming back, a powered anode is the durable answer.
If you hire a plumber
A plumber charges in the low hundreds for an anode swap and flush. Beware anyone upselling a big water-treatment system for what's usually an anode-rod fix.
DIY — Moderate Gas pilot light won't stay lit The classic gas-unit failure
Symptoms
- Pilot lights then goes out when you release the knob
- No hot water on a gas unit
- Repeated relighting needed
Likely cause
Almost always a failing thermocouple (or flame sensor on newer units) — the safety device that senses the pilot flame and shuts off gas if it doesn't 'see' one. A dirty pilot orifice can also cause it.
The part
Thermocouple (or flame sensor)
$10–$20
Home Depot/Lowe's; thermocouple ~$10-$20
Difficulty
Replacing a thermocouple is a recognized moderate DIY job — it's a cheap part and a few connections — but it involves the gas burner assembly, so you must shut off the gas and work carefully. If you're not comfortable around gas, this is a reasonable one to hand to a pro.
⏱ 30-60 minutes
🔧 Wrench/nut driver · Screwdriver
GAS: shut off the gas control valve before working. If you smell gas at any point, stop, leave, and call the gas company. Don't force-relight.
A pilot that won't stay lit is almost always a $15 thermocouple. Handy and comfortable with gas? Do it yourself. Not comfortable with gas? It's cheap enough to hand off — no shame in that.
DIY vs. Pro
A handy person can absolutely replace a thermocouple for a couple of bucks. But it's gas, so if you have any hesitation, this is a cheap-enough pro job that it's not worth the stress. Either way, it's a repair, not a replacement.
If you hire a plumber
A plumber typically charges in the low-to-mid hundreds for a thermocouple replacement — much cheaper than a new heater.
When repair doesn't make sense
If the tank is leaking from the body, is more than 10–12 years old, or keeps needing repeated repairs, replacement is often cheaper long-term. See installed pricing and local permit requirements for your city: