Tankless Water Heater Clicking Noise
The Short Answer: A tankless click is usually DSI spark, a gas-valve solenoid, an electric contactor, or a recirc check valve — not a healthy fan hum. Tick-tick then silence with ice water is a failed ignition trial. One listen with the cover on. Do not keep clicking fuel into a dark burner. Smell gas, leave.
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Search Intent & The Real Problem
You opened a hot faucet. The closet ticks. Sometimes you get fire. Sometimes you get a code and a cold shower. People search “clicking noise” for four machines: gas DSI spark, electric contactors, a recirc spring-check, and a lockout that is still trying. A light tick at light-off that becomes blue flame is normal spark. Rapid ticks that never become flame is burner not lighting physics on a tankless chassis. A 60 Hz drone with good hot water is humming, not this page. A metronome after the shower is often ticking like a clock.
Portable gas boxes: Marey not igniting. RV DSI: Atwood clicking. Tank Honeywell spark: igniter no spark.
What other guides get wrong
They call every click “sediment,” which is a tank diagnosis. Tankless units do not have a 40-gallon pile of rocks. They tell you to reset until the spark catches. Ten trials glaze the igniter and flood the burner. They paste a standing-pilot piezo ritual onto a 199 kBTU DSI. And they treat electric contactor chatter as “normal relay noise” while a chamber is grounding and a breaker is about to open.
Step-by-Step Troubleshooting
Step 1: Name the click — fuel, when, and whether you have flame
| When it clicks | Likely source | Hot water? |
|---|---|---|
| 1–3 ticks at the start of a hot call, then a whoosh of flame | Normal DSI spark | Yes — leave it |
| Rapid tick-tick, then silence, ice at the tap | Spark, no flame, or lockout | No — this page |
| Click, bang, then dark | Delayed ignition | Shut down |
| Click every few seconds with no one using water | Recirc, leak, or freeze heat | Maybe — find the flow |
| Heavy clack on electric units as flow starts | Contactors / relays pulling in | Yes if chambers heat |
| Chatter, then a tripped double-pole | Grounded chamber or dying contactor | No — lock it off |
| Soft tick in the pipes after the shower | Check valve / expansion | Yes — different part |
- What to look for: Rating plate: gas RTG / RU / NPE / T-K vs electric RTEX / EcoSmart / Powerstar. Photo of any code before you kill power. Cover stays on for the first listen.
- Required tools: Ears, one helper at a faucet, flashlight on the plate.
Step 2: Gas DSI — spark vs no flame vs lockout
- What to look for: Appliance cock parallel to the pipe. Other gas appliances lighting. LP not empty; a frosted first-stage regulator starves the trial. Fan must spin before spark on a vented indoor unit; a silent blower is carbon monoxide if anything burns — blower not working. Spark you can hear with a dark burner: no gas at the valve, wrong NG/LP, or a solenoid that never opens. Spark, brief blue, then a 12 or 11: flame rod or lost proof — Rinnai 12, Rheem 11. No spark at all on a click: electrode, harness, or board — still not a homeowner gas-valve swap.
- Required tools: Ears and eyes. One trial. Manometer work is licensed (NG ~3.5–7 in. w.c. / LP ~10–11 in. w.c. — confirm the rating plate).
Do not crack a flare to “see if you have gas.” Do not purge fittings. Exhaust that smells like fuel: tankless exhaust gas smell. A bang is loud bang — shut it down.
Step 3: Electric tankless — contactors, not spark plugs
- What to look for: Whole-house electrics have no burner. The click is a relay or contactor staging a 240 V chamber. One solid clack as flow hits activation (~0.3–0.5 GPM on many residential units — your sticker wins) is normal. Rapid chatter is low flow hunting the activation threshold, a dying coil, or a module that is grounding. A click then a breaker in the middle is keeps tripping — lock every heater breaker off. Oscillating heat with relay chatter is often the mixing valve pinching flow — hot then cold.
- Required tools: Panel from a dry location. Cover off only with all double-poles locked and 0 V at the lugs.
A 4500 W / 240 V tank element is ~18.8 A and ~12–13 Ω dead. These chambers are several times that load. Do not ohm them live. Do not jumper a thermal cut-out because the relay “won’t stay in.”
Step 4: Recirc, freeze protection, and a click that is not ignition
- What to look for: Onboard pump (RUR / Navien A-series ComfortFlow) clicking on a schedule with no one in the house: recirc timer, not a failed igniter. A unit that never sleeps will click all day on a 0.4 GPM weep. Outdoor gas box in January: freeze-protection solenoids or ceramic heaters ticking with power on — that is survival, not a defect, until you hear water. Isolation-valve packing drip or a toilet fill valve is enough flow to wake DSI. Packed inlet screen makes the turbine chatter and the board never sees a clean call.
- Required tools: Recirc off for a 24-hour test if you have a switch. Eyes on the inlet screen with water isolated. No compressed air through a flow transducer.
House static over ~80 psi belongs on a PRV, not on the igniter. T&P, if fitted, is typically 150 psi / 210°F — never cap it because the discharge “ticks” in the pan.
Step 5: One trial, one code, then stop
- What to look for: Cause addressed (cock open, LP not frozen, recirc off for the test, screen rinsed). One hot-water call with the cover on. Clean spark, stable flame, no bang, no repeating click-lockout. Same tick-tick-dark on the next call is the end of DIY. Inlet grit causes no-fire more often than a “bad clicker.” Do not sandpaper a flame rod into a needle. Microamps and manifold pressure are licensed.
- Required tools: Your hand on the faucet and the appliance switch. No paperclip in the PCB.
Standing-pilot tanks with a red button are a piezo, not a tankless DSI.
When DIY Ends: Calling a Licensed Pro
You may confirm the shutoff, hear whether spark becomes flame, kill recirc for a test, rinse an inlet screen with water off, and power-cycle once after a code. Stop at gas odor, delayed-ignition bangs, a silent combustion fan, a clicking electric box that trips a breaker, a wet cabinet, and any gas-valve or live-contactor work. A licensed plumber or electrician will measure flame current or 240 V staging, not guess from the closet door.
Frequently Asked Questions
Q: Why is my tankless water heater making a clicking noise? A: Gas units click at DSI spark and at the gas-valve solenoids. Electric units click contactors. Recirc check valves and freeze-protection parts click without a shower. Tick-tick then ice water is a failed ignition trial, not a lifestyle noise.
Q: Is clicking on a tankless normal? A: A short tick at the start of a hot call that becomes flame is normal spark. Rapid ticks with no flame, a bang, or a tripped breaker are not. One failed trial, then a licensed tech.
Q: Why does the tankless click when no one is using hot water? A: Recirc pump or timer, freeze protection, or a small flow (leak, toilet, isolation valve) that is enough to wake the turbine. Kill recirc for a day. If it still fires, find the flow — do not keep resetting a lockout.