Seven Sounds Your Building Shouldn't Be Making
Photo: After Clifford Henry Mecham, Public domain, via Wikimedia Commons
Every experienced building services engineer develops a kind of auditory sonar. Walk into enough plant rooms and you stop hearing noise and start hearing information. The trouble is that most people responsible for commercial buildings — facilities managers, landlords, office managers pressed into duty — haven't had years of plant rooms to calibrate against.
So consider this your field guide. Seven noises, what they mean, and what ignoring each one is likely to cost you. Urgency ratings are ours, based on how often we've seen each one turn into a Friday-afternoon emergency.
1. The Kettle: Rumbling Boilers
The sound: A deep, rolling rumble, like a kettle a fraction away from boiling.
The diagnosis: Kettling. Scale or sludge on the heat exchanger is trapping water against hot surfaces, where it flashes to steam and collapses with a rumble. Common in hard-water areas and systems with patchy water treatment history.
Urgency: Moderate. A kettling boiler is working harder than it should, wasting energy and shortening its own life.
Cost of ignoring: Reduced efficiency of 5–10% on that boiler's gas consumption, and a heat exchanger replacement (£3,000–£8,000 installed) arriving years early. A chemical flush and water treatment review now is a fraction of that.
2. The Gravel Truck: Failing Fan Bearings
The sound: A grinding or growling from an AHU or rooftop unit that gets worse week by week.
The diagnosis: Bearing wear on a supply or extract fan. The bearing is telling you it is dying. Fans are considerate like that — they give months of warning.
Urgency: High — but not today. Schedule replacement within weeks.
Cost of ignoring: A seized bearing can take the fan shaft and motor with it. A planned bearing swap might cost £500–£1,500; a seized assembly with motor damage can triple that, plus the cost of a ventilation-dependent building with no airflow until parts arrive.
3. The Cannon Shot: Water Hammer
The sound: A single, startling bang from the pipework, often when a valve closes.
The diagnosis: A pressure surge in legacy pipework — usually a fast-closing solenoid or zone valve slamming shut on a column of moving water. In older commercial buildings with original steel distribution, it is remarkably common.
Urgency: Moderate to high. One bang is an annoyance. Repeated bangs are fatiguing joints and welds.
Cost of ignoring: A burst legacy main in a ceiling void or riser. Depending on location, you are into five figures very quickly — and if the pipework is original, insurance assessors will ask pointed questions about maintenance history.
4. The Whistle: Cavitation in Pumps
The sound: A high-pitched whine or hissing from the pump set, like air being sucked through a pinhole.
The diagnosis: Cavitation — the pump is starved of water or suction pressure and is boiling it at the impeller instead. Those tiny steam bubbles collapse against the impeller and pit the metal.
Urgency: High. Cavitation destroys pumps with genuine enthusiasm.
Cost of ignoring: A replacement commercial circulator runs £1,500–£5,000. Fixing the underlying cause — a blocked strainer, a mis-set valve, low system pressure — often costs less than £300.
5. The Click of Doom: Contactor Chatter
The sound: Rapid, buzzing clicking from a control panel or plant enclosure.
The diagnosis: A worn or loosely-wired contactor repeatedly failing to hold. Left alone, it burns out the contacts and takes the motor's starting circuit with it.
Urgency: High, and cheap to fix. This is the best value repair on the list.
Cost of ignoring: A new contactor is a £150 job. A burnt-out motor starter, or a chiller that won't start in a heatwave, is not.
6. The Drip-Tick: Expansion Vessel Trouble
The sound: Not a noise so much as a rhythm — the pressure gauge ticking down and the filling loop being topped up, again and again.
The diagnosis: A failed expansion vessel bladder. The system loses pressure, the PRV discharges, and somebody keeps repressurising it. We have seen this cycle run for months before anyone investigates.
Urgency: Moderate. But every discharge of the pressure relief valve is a small corrosion event for the system water.
Cost of ignoring: Progressive system corrosion, sludge, and eventually the kettling boiler from item one. These noises are related, and that is rarely a coincidence.
7. The Silence
The sound: Nothing at all, where there used to be something.
The diagnosis: The most expensive sound in facilities management. A pump or fan that has stopped, a BMS alarm that has been muted rather than investigated, a plant item that has been quietly switched off by someone who didn't like the noise.
Urgency: Immediate. Silence in a plant room deserves the same attention as a bang.
Cost of ignoring: Unquantifiable, and usually discovered by a tenant.
Listen Before It Shouts
None of these noises require an engineering degree to notice — only a willingness to walk the plant room occasionally and pay attention. Encourage your team to report odd sounds rather than adapt to them. The buildings that age well are the ones where somebody heard the gravel truck in March, not November.
