Bosch Tankless Water Heater noise diagnosis in Greater Vancouver

A tankless water heater is a small combustion appliance bolted to a wall, and walls carry sound. A Bosch unit in a Burnaby laundry room can sound alarming from the hallway and completely ordinary once you stand in front of it with the door open. Get close before you decide something is broken.

Sound is a starting point, not an answer. The same clunk can be a burner lighting off the way it always has, a check valve slamming in copper pipe two metres away, or a mounting bracket that quietly lost a screw. What separates them is timing. Does the noise land the instant a tap opens, twenty seconds in, at shutdown, or nonstop while the unit sits idle?

This walks the sounds the way a technician walks them on a Lower Mainland service call. What each noise generally indicates, what gets checked and in what order, what you can safely look at yourself, and the point where the right move is to shut the unit down and phone HeatLand at (604) 330-3812.

Listen first: pin the sound to a moment in the cycle

Open a hot tap and stand at the unit. A tankless heater runs a short, repeatable sequence every time, and each stage has its own signature. Flow switch or sensor registers water moving. Fan spins up and purges the heat exchanger and vent. Igniter fires. Burner lights. Modulation settles the flame to match the draw. Tap closes, burner shuts off, fan runs a post-purge, everything stops.

Write down which of those moments your noise attaches to, because that single detail eliminates most of the possibilities before anyone touches a tool. A bang at the moment of light-off is a combustion question. A bang half a second after you close the tap is almost certainly plumbing, not the heater. A hum that continues after post-purge ends is electrical. A squeal that only appears when two showers run at once is flow-related.

Also pin the location. Put a hand flat on the cabinet, then on the vent pipe, then on the copper lines feeding it. Vibration transmits, and in older Vancouver houses with joist-mounted pipe and thin utility-room walls, the loudest spot is often nowhere near the actual source. Note the display too. If a code appears, read it off the unit and check it against that unit’s own manual or the label inside the cabinet, because code meanings differ by brand, model and year.

Banging and booming at ignition: delayed light-off

A single hard thump when the burner lights is the sound most worth taking seriously. In general terms, it means gas entered the combustion chamber and did not ignite immediately. When it finally does catch, it burns the accumulated gas all at once instead of lighting smoothly at the burner face. Technicians call it delayed ignition, and it is a combustion issue, not a plumbing one.

The general causes sit on both sides of the burner: something wrong on the gas side (supply pressure sagging under load, a partially restricted gas train), something wrong on the ignition side (a fouled or misaligned igniter, a weak spark), or something wrong on the air side (a partially blocked intake or exhaust, a fan not reaching speed, a dirty burner surface disrupting the flame spread).

Salt air matters here. Units venting through an exterior wall in White Rock, Steveston or the North Shore waterfront corrode faster around terminations, and a screen fouled with corrosion product or spider webbing changes airflow long before anything looks dramatic.

This is not a homeowner repair. Diagnosing it correctly means manometer readings on the gas line under load, combustion analysis at the vent, and inspection of the burner and igniter with the unit powered down and gas isolated. That is TSBC-certified gas fitting work. If the banging is loud, repeating, or accompanied by any burnt smell, stop using the unit and book service.

Banging you hear in the walls: water hammer, not the heater

A bang that lands right after a tap or appliance shuts off is usually the plumbing, and it is one of the most common false alarms on a tankless service call. Water moving through a pipe has momentum. Close a valve fast enough and that column of water stops against the closed valve, and the shock travels through the piping as a loud knock.

Tell it apart from combustion noise by testing it deliberately. Run the hot tap, then close it quickly. Bang. Now close it slowly over three or four seconds. If the bang disappears, the heater is fine and you have water hammer. Then repeat with a cold-only fixture. If cold-only closure bangs too, the tankless unit is not involved at all, since it never fires on a cold draw.

The usual contributors are fast-closing solenoid valves in washing machines and dishwashers, loose pipe strapping in a joist bay, missing or waterlogged arrestors, and high incoming municipal pressure. Older Lower Mainland housing stock frequently has long unsupported copper runs that amplify the knock through the framing.

Fixes are plumbing-side: securing loose pipe, adding or replacing arrestors near the offending fixture, or checking whether the house needs pressure regulation. None of it involves the heat exchanger. Worth sorting out anyway, because sustained hammer is hard on every fitting in the house, including the ones feeding your Bosch unit.

Rattling and buzzing: loose hardware and vent sections

Rattle is mechanical. Something is loose and the fan or the burner is shaking it. The good news is that rattle is the one noise family where careful homeowner observation actually narrows things down, because the sound changes when you touch the part that is vibrating.

With the unit running, rest a hand lightly on the front cover. If the rattle drops away, the cover screws or clips are loose or a gasket has flattened. Move to the vent pipe next. Concentric and two-pipe venting is assembled in sections with clamps and gaskets, and a section that has crept loose will buzz in sympathy with the fan. Then the mounting bracket and the wall itself. A unit hung on strapping instead of solid blocking can drum the whole wall cavity, which is exactly the complaint that gets escalated in strata buildings where the neighbour hears it through shared framing.

Inside the cabinet is a different story. A rattle that persists when everything external is snug can be fan blade damage, debris that found its way through the intake, or a component loosening on its mount. That requires opening a sealed combustion appliance, which is where homeowner troubleshooting ends.

Do not solve rattle by wedging padding against a vent pipe or blocking any part of an intake or exhaust. Clearances around venting exist for combustion and CO safety, and improvised damping has caused far worse problems than the noise it silenced.

Humming and buzzing: the electrical family

A steady hum is usually electrical, and the first question is whether it tracks with the fan or exists independently of it. Trigger a hot draw and listen to the spin-up. Fan-related hum rises and falls with fan speed, changes as the unit modulates, and stops when post-purge ends. That pattern points at the fan motor and its bearings, or at the blower wheel loaded with dust and lint in a laundry-room installation.

A hum that sits at a constant pitch regardless of fan speed, and continues when the unit is idle but powered, is a different animal. Transformers and solenoid coils hum at line frequency. A gas valve solenoid energizing produces a brief buzz that is entirely normal on many units, so a short buzz at the moment of light-off is not automatically a fault.

What makes it worth a service call is change. A hum that got louder over a season, a hum that developed a grinding or warbling edge, or a hum accompanied by the unit locking out mid-shower all point to a component moving toward failure rather than a normal operating sound.

There is one thing you should check yourself, and it costs nothing: is the hum actually coming from the heater? Recirculation pumps, nearby transformers and adjacent appliances all hum. Kill power to the heater at the breaker for a moment and listen. If the sound continues, look elsewhere before spending money on the water heater.

Squealing, whistling and screeching: restriction somewhere

High-pitched noise generally means a fluid is being forced through a passage that is smaller than it should be. Air, water or gas — the physics is the same, and the job is figuring out which one.

Whistling that appears only during a hot draw and scales with how far you open the tap is water-side. Common general causes are a partially closed isolation or service valve left half-shut after previous work, a fouled inlet screen, a fixture cartridge, or a mixing valve throttling flow. Try one fixture at a time. If the whistle exists on a single fixture only, the fixture is the suspect, not the heater.

Whistling that starts with fan spin-up before ignition and is independent of how much hot water you draw is air-side. Intake or exhaust restriction, a terminal screen fouled with debris, or a bird or rodent nest at an exterior termination. This one earns a same-week service call rather than a shrug, because anything restricting a combustion appliance’s air path is a safety matter, not just a comfort one.

A metallic screech that comes and goes with fan speed leans toward a failing motor bearing.

A sustained hiss near the gas connection is not a noise problem to diagnose. Leave the home and call the gas utility and a licensed technician from outside. Do not check it with a flame, and do not operate light switches on your way out.

Clicking, ticking and gurgling: mostly normal, sometimes not

Not every sound is a fault, and replacing a healthy unit because it makes noise is an expensive mistake. Rapid clicking at the start of a cycle is typically the igniter doing its job, and on many units you will hear a distinct series of clicks followed by a soft whoomph as the burner lights. If the clicking stops as soon as the burner catches, that is the sequence working.

Clicking that repeats several times without the unit ever producing hot water is the opposite: it is trying to light and failing, and it will usually end in a lockout code. Read the code off the display and check it against your own unit’s manual. Do not reset repeatedly to force it through — a lockout is a safety function doing what it was designed to do.

Ticking during and after a run is often thermal expansion. Metal heats, grows, and slides slightly against its mounts, then contracts as it cools. It is common in the minutes after a long shower and generally harmless.

Gurgling and trickling deserve a look. Condensing units produce acidic condensate that has to drain freely, and a partially blocked condensate line, a dry or improperly installed trap, or a neutraliser that has spent itself can all produce gurgling. Standing condensate is corrosive and does real damage over a Vancouver winter, so have the drain path checked.

Water quality, recirculation and what a HeatLand tech does on site

Metro Vancouver water is soft and low in dissolved minerals, so the heavy scale problem people import from hard-water regions is less of a factor here than the internet suggests. That does not make maintenance optional. Soft, slightly aggressive water plus older galvanized or mixed-metal piping in pre-1980s housing stock moves sediment and corrosion debris downstream, and a heat exchanger and its inlet screen are effective filters whether you want them to be or not. Restriction there shows up as flow noise and short-cycling before it shows up as a code.

Recirculation adds its own soundtrack. Pumps hum, timers and aquastats start and stop the loop at odd hours, and a loop with air trapped in it will gurgle and knock until it is purged. If your noise happens when nobody is using water, the recirculation loop is the first place to look.

On a HeatLand call, the order is deliberate. Confirm the sound with you present, since intermittent noise is the hardest thing to chase after the fact. Read any stored codes and check them against the unit’s own documentation. Verify venting and intake integrity and clearances. Check gas supply pressure under load and run a combustion analysis. Inspect the burner, igniter, fan and heat exchanger. Check water flow, filter screens, isolation valves and condensate drainage. Then explain what we found, what it means, and what it will take to fix — in writing, no obligation. Call (604) 330-3812.

Quick Checklist

• Note exactly when the noise happens: at tap-open, during fan spin-up, at ignition, mid-run, or after shutdown.
• Test for water hammer by closing a hot tap fast, then slowly, then repeating with a cold-only fixture.
• Read any code directly off the unit’s display and verify it against that unit’s own manual or the cabinet label — never a generic list.
• Check that isolation and service valves are fully open, and that no fixture is partly closed or fitted with a clogged aerator.
• Look at the exterior vent termination for debris, nesting, or corrosion buildup — especially on salt-air-exposed Lower Mainland walls.
• Stop and call for service if you hear a hard bang at ignition, a sustained hiss near the gas line, or repeated lockouts.

Frequently Asked Questions

Reviewed by the HeatLand Heating & Cooling team — licensed, insured, TSBC-certified HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. Error codes, specifications, pricing and rebate programs vary by model and change over time; confirm details against your unit’s own manual, a written quote, and the manufacturer or CleanBC/FortisBC. If you smell gas or your CO alarm sounds, leave the home and call the gas utility and a licensed technician from outside.