Water Heater Ticking Like a Clock?
The Short Answer: A metronome tick at the heater is usually copper growing against a strap, a recirc spring-check fluttering, a heat-trap nipple, or a tankless relay/fan after the shower. It is not “ignore it.” A tick that is actually a drip hitting the pan is a leak. A tick with a gas smell or a bang is a shutdown.
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Search Intent & The Real Problem
You hear tick… tick… tick from the closet or the ceiling after someone ran hot water. Forums say expansion is normal and to live with it. Copper does grow as it heats — about 1 inch per 100 feet per 100°F — and a tight strap will click. A failing check valve on a recirc loop will click all night. A tankless post-purge will click once, then the fan will run about a minute. You name the clock before you buy a tank.
Different noises, different pages: Navien knocking, Rinnai humming, hissing after a shower.
What other guides get wrong
They say every clock-tick is “harmless pipe expansion” and to go to bed. Expansion against a strap is one cause. A recirc check that chatters at 2 a.m. is a failed part. Drops from a T&P overflow hitting a pan sound like a clock until the floor is wet. They also tell you to flush sediment for a tick that is clearly in the copper, not the tank.
Step-by-Step Troubleshooting
Step 1: Time the tick — that is the diagnosis
| When it ticks | Likely source |
|---|---|
| Only while the tank recovers, along the hot copper, then stops | Pipe expansion against straps / plates |
| Steady tick with no recovery, recirc pump running | Spring check or flow-check flutter |
| One click after the shower, then a faint fan | Tankless post-purge relay / damper |
| Tick in the pan, wet spot growing | Drip — T&P, drain, gasket, not “noise” |
| Tick then a sizzle after a long shower | Sediment on the element/burner — hissing after shower |
| Single click, then quiet, electric tank | Thermostat opening at setpoint — not a clock |
- What to look for: Whether it tracks a heat call, a recirc schedule, or a drip.
- Required tools: Phone stopwatch, flashlight, a dry paper towel in the pan.
Step 2: Pipe expansion and heat-trap nipples
- What to look for: Copper touching a wood plate, a tight two-hole strap, or a joist. Dielectric nipples with plastic heat-trap inserts that click as flow starts. PEX moves less; if you “hear the heater” in a PEX house, look at the check valve and the tank, not the tube.
- Required tools: Eyes on the first 10 feet of hot. Do not start loosening unions on a live tank.
A strap click that started the day after a new heater is often the new copper run, not a defective tank. A strap click that started after years is still a strap — unless the pan is wet.
Step 3: Recirc check valve — the all-night clock
- What to look for: Dedicated recirc return, or a crossover under a sink. Spring check at the heater ticking in time with the pump. Waterlogged expansion tank (Schrader spits water) making the check hunt. House static over 80 psi making every check noisy.
- Required tools: Hose-bib gauge, tire gauge on the expansion tank. Pump off for a test: if the clock dies with the pump, the check or the pump is the job.
A failed check that lets hot bleed into cold is a crossover, not a tick to ignore. Lukewarm cold water at a far fixture is the clue.
Step 4: Tankless clicks are relays, not rocks
- What to look for: Click at the start of a hot-water call (water valve / igniter), click at the end (post-purge). Rapid click-click-click with no flame is ignition lockout — photograph the code, one power cycle, same rule as a Takagi reset. Do not keep sparking.
- Required tools: Phone photo of the controller. Cover stays on.
Step 5: When the “tick” is water or combustion
- What to look for: Bead at the T&P discharge, Rheem plastic drain, wet jacket. Delayed-ignition tick-bang on a gas tank — shut the gas cock; do not purge the line.
- Required tools: Paper towel. If it is a leak, treat it as a leak.
When DIY Ends: Calling a Licensed Pro
Stop if the pan is wet, you smell gas, the tick is a bang, or a recirc check is on a live hot line you cannot isolate. You may loosen a crushing strap on cold pipe, gauge a hose bib, and photograph a tankless code. You may not oil fans, cap a T&P, or keep resetting a click-no-light gas valve. A clock you cannot name in five minutes is a licensed visit, not a sleep aid.
Frequently Asked Questions
Q: Why does my water heater tick like a clock? A: Copper expanding against a strap, a recirc check valve fluttering, a heat-trap nipple, a tankless post-purge relay, or drops hitting the pan. Time it. A drip is not a noise.
Q: Is a ticking water heater dangerous? A: Expansion clicks are annoying, not a fire. A tick that is a leak, a gas-valve chatter with odor, or a delayed-ignition bang is dangerous. Shut it down and hire a licensed tech.
Q: How do I stop a water heater from ticking? A: Name the source first. Free a crushing strap, replace a chattering recirc check, fix pressure/expansion if the T&P is dripping, or service the tankless. Do not “flush sediment” for a tick in the copper.