Stepping into a shower that is unexpectedly freezing—or worse, dangerously scalding—is one of the most jarring experiences of homeownership. It immediately triggers worry: Is the water heater broken? Do I need to replace the whole unit? How much will this cost?

Looking for more guidance? Take a look at our Repairs overview.

Take a deep breath. While water temperature issues are inconvenient, they don't always mean your water heater is dead. Often, the problem is a simple setting that drifted, a pilot light that went out, or a tripped breaker.

In this guide, we will help you isolate the problem. We’ll start by checking if the issue is with a single faucet or the whole house, and then walk through the specific adjustments for your type of water heater.

What These Symptoms Usually Mean

Before you grab a wrench, let’s look at what the water is telling you.

• Water is lukewarm or cold everywhere: This usually means the heating element isn't engaging (tripped breaker or pilot light out) or the thermostat is set too low.
• Water is way too hot everywhere: Your thermostat is likely set too high (above 120°F) or, in rare cases, a valve is stuck.
• Water is wrong at only one faucet: This is almost never a water heater problem. It’s likely a localized issue with that specific sink or shower valve.

Step 1: Is It One Fixture or the Whole House?

This is the most critical diagnostic step. Go to a different room and turn on the hot water.

If the water is fine in the kitchen but cold in the shower: The problem is local. You likely have a mixing valve issue or a clogged aerator at that specific fixture.

• Safe to try yourself: Check underneath the sink to ensure the shut-off valves are fully open (turned counter-clockwise). You can also unscrew the aerator at the tip of the faucet to rinse out debris.
• When to call a pro: If cleaning the aerator doesn't work, you may need a plumber to replace the cartridge or mixing valve inside the faucet handle.

If the water temperature is wrong everywhere: The issue is at the source—your water heater. Proceed to the steps below based on what kind of heater you have.

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Step 2: Identify Your Water Heater Type

Look at your unit.

• Tank (Gas): Has a large metal cylinder and a gas control valve/dial near the bottom.
• Tank (Electric): Has a large metal cylinder but no gas dial; has panels covering electrical components.
• Tankless: A small box mounted on the wall; no large storage tank.
• Solar: Has a storage tank connected to roof panels and a mixing valve on the pipes.

Find your type below for specific instructions.

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For Gas Tank Water Heaters

If the water is too hot:

1. Locate the gas control valve near the bottom of the tank.
2. Turn the dial toward "Warm" or the 120°F mark.
3. Wait about two hours for the water to cool naturally, then test a faucet.

If the water is too cold:

1. Check the dial. Is it set to "Hot" or around 120°F? If not, adjust it.
2. If the dial is correct but water is cold, check the pilot light. Remove the lower access panel and look through the sight glass.
3. No flame? You need to relit the pilot. Turn the knob to "Pilot," hold it down, and use a long-nose lighter at the opening. Once lit, hold the knob for a minute, then release and turn to "On."
4. Flame is on? If the pilot is lit but the burner won't ignite to heat the water, the issue is likely a faulty thermostat or gas valve.

• When to call a pro: If you cannot get the pilot light to stay lit after multiple tries, or if you smell gas (leave the house immediately), call a professional.

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For Electric Tank Water Heaters

If the water is too hot:

1. Go to your electrical panel and flip off the water heater breaker.
2. On the tank, use a screwdriver to remove the upper metal access panel and pull back the insulation.
3. Use a flathead screwdriver to turn the thermostat dial down to 120°F.
4. Replace the insulation and cover, then flip the breaker back on.

If the water is too cold:

1. Check your electrical panel. Is the breaker tripped? If so, flip it off and back on.
2. If the breaker is fine, turn it off anyway for safety.
3. Open the upper access panel on the tank and pull back the insulation.
4. Look for a red "Reset" button on the thermostat. Press it firmly until it clicks.
5. Replace the cover, turn the power back on, and wait 45 minutes.

• When to call a pro: If the breaker keeps tripping or the reset button pops out again shortly after resetting, you likely have a bad heating element or electrical short.

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For Tankless Water Heaters

If the water is too hot:

1. Find the digital control panel on the unit.
2. Press the "Temp Down" button until it reads 120°F.
3. Run the water for a minute to clear the line and test the new temperature.

If the water is too cold:

1. Check that the unit has power (electric) or gas supply (gas).
2. Locate the cold-water inlet filter on the bottom of the unit.
3. Turn off the isolation valves, unscrew the filter, rinse out any debris, and reinstall.
4. If that fails, hold the "Reset" button on the control panel for 5 seconds.

• When to call a pro: Tankless units are complex. If cleaning the filter and resetting the electronics doesn't work, internal sensors may be failing.

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For Solar-Assisted Water Heaters

Solar systems usually have a "mixing valve" (or tempering valve) on the pipes near the storage tank. This valve mixes scalding solar-heated water with cold water to make it safe.

1. Locate the mixing valve.
2. Turn the cap slightly clockwise to make water hotter, or counter-clockwise to cool it down.
3. Wait 30 minutes before testing.

• When to call a pro: Solar systems involve pumps and complex controls. If the valve adjustment doesn't work, call a technician.

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Time and Cost Expectations

Diagnosing these issues is usually free and fast. If you need repairs, here is what to expect:

• DIY Adjustment: $0 | 10–30 minutes
• Replacing a Heating Element or Thermostat (Pro): $150–$300 | 1–2 hours
• Relighting a Pilot Light (Pro): $100–$200 | 1 hour
• Tankless Maintenance/Descaling: $150–$250 | 1–2 hours

What to Do Next

If you've adjusted the settings and reset the breakers but the water temperature is still erratic, it's time to stop troubleshooting and bring in help. Water heaters involve high voltage, gas lines, and pressure vessels—if the simple fixes don't work, the risks of DIY repair outweigh the savings.

Keeping track of when you last flushed your tank or checked the anode rod can prevent these surprises. For help organizing your home maintenance history and reminders for simple checks like these, download the Casa app. It’s a great way to stay ahead of repairs so you aren't left taking a cold shower.