Water heater not working? Diagnose it in 5 minutes before you call.

Master plumber, Dillsburg, PA. Updated April 2026. This is the same triage flow we use over the phone before dispatching a truck. Most no-hot-water situations come down to one of four things, and you can usually identify which one in under 5 minutes.

Featured image: Photo by bhagya laxmi on Unsplash

Photo by bhagya laxmi on Unsplash

Step 1. Safety check first

Before you touch anything, do this check. If any of these are true, stop and call us at (223) 200-3488 right now:

• You smell gas anywhere near the heater.
• Water is actively pooling under or around the tank.
• The flue (the metal vent on top) is rusted through or disconnected.
• The T&P relief valve is dripping or hissing.
• The tank shell is bulging or scorched.

None of those? Continue.

Step 2. Identify the symptom

1. No hot water at all. Heating system has stopped working entirely.
2. Lukewarm water. Heater runs but can't reach setpoint.
3. Hot water runs out fast. Tank can't keep up with demand it used to.
4. Water heater is leaking. Visible water on the floor or down the side.
5. Strange noises. Popping, banging, hissing, or whistling.

Step 3. Gas tank water heaters

No hot water

Pull the burner cover. Look at the pilot. Three possibilities:

• Pilot is out. Try to relight per the label. If it lights but won't stay on after holding the button, the thermocouple is failing. Lifespan: 5 to 8 years. Replacement is straightforward but requires a small wrench and a new thermocouple matched to the heater.
• Pilot is on but main burner won't fire. Gas valve is bad. This is a $300 part, 2 hours of labor. Worth doing only if the tank is under 8 years old.
• Pilot won't light at all. Either no gas to the heater (check shutoff valve and meter) or a clogged pilot tube.

Lukewarm water

Tank is making heat but not enough. Most common: the dip tube has broken off and cold water is mixing with hot at the top of the tank. Less common: thermostat is set wrong (should be 120 to 125 degrees Fahrenheit). Even less common: hard-water sediment has filled the bottom 1/3 of the tank.

Tank is leaking

If water is coming from the T&P valve, the valve is doing its job - the tank is over-pressurized or over-temperature. If water is coming from the bottom of the tank shell, the tank is rusted through and not repairable. Replace it. Hot water heaters in Dillsburg average 9 to 11 years.

Step 4. Electric tank water heaters

No hot water

Check the breaker first. Electric tanks are on a 30-amp double-pole breaker. If it's tripped, do not just reset it - find out why it tripped. Common cause: a heating element has shorted to the tank shell. Replacement element: $35 part, 90 minutes of work.

Lukewarm water

Electric tanks have two elements (upper and lower). When the lower element fails, you get lukewarm water - the upper element keeps the top of the tank hot but it can't keep up. When the upper element fails, you get NO hot water. We test elements with a multimeter at the tank.

Step 5. Tankless water heaters

Tanklesses don't behave like tanks. If yours stopped working, look for an error code on the front panel display. The major brands (Rinnai, Navien, Rheem, Noritz) all have unique codes:

• Code 11 on Rinnai/Navien: ignition failure. Usually gas supply or vent issue.
• Code 12: flame failure. Often dirty flame rod, sometimes wrong gas pressure.
• Code 14: overheat. Heat exchanger has scale - it needs descaling.
• Code 16: high temperature shutdown. Same as 14, often.
• Code 99: vent obstruction or condensate drain blockage.

If your unit shows a code, write it down before calling. Saves us a 20-minute on-site diagnosis.

Step 6. When to stop and call a plumber

Call us if:

• You smell gas at all - call from outside the building.
• The tank is over 10 years old AND you're getting symptoms - replacement is more cost-effective than repair.
• Multiple symptoms (lukewarm + noise + dripping T&P) suggest the tank is failing.
• You don't feel comfortable testing electrical components or replacing a thermocouple.
• The unit is under warranty - DIY work voids many warranties.

FAQs

Related reading: How long do water heaters last? · Tankless vs tank · Water heater repair service · Tankless install