Boiler Making Noise: Kettling, Banging, Gurgling, Whistling

Gurgling: air in the system

What it is. Weil-McLain’s troubleshooting table says radiators or baseboard that are noisy because of air in the system are fixed by bleeding the air through their vents. Viessmann says gurgling is caused by air in the radiators, and Lochinvar lists air in the piping as a cause of noisy operation.

The fix. Bleed the radiators or baseboard the way the makers describe: how to bleed a radiator. Viessmann warns the escaping air may be hot, so keep your hand and face clear. Then check the pressure gauge, because bleeding lets some water out. Never bleed a steam radiator: Castrads says its vent lets the air out by itself.

A noisy pump. Grundfos says air in its ALPHA2 pump may make a noise that stops after a few minutes of running, and that the system cannot be vented through the pump. Taco says loud water noise from a 007e with a flashing white light means air in the system, and the system should be vented.

Popping or rumbling inside the boiler

What it is. Weil-McLain’s tables call it a popping or percolating noise in the boiler. The first cause they give is mineral deposits from constant use of fresh make up water. People call this kettling, because it sounds like a kettle coming to a boil.

Why it happens. A leak lets water out, the fill valve tops it up with fresh water, and that water brings in minerals. Weil-McLain says those minerals build up in the boiler, overheat the metal and can cause section failure.

Weil-McLain’s other causes. The wrong pH in the boiler water, and too little water flowing through the boiler. Lochinvar’s chart for a noisy Knight also lists low water flow through the heat exchanger, and its fix is to check the boiler and system pumps are running on a call for heat.

What you can do. Look for drips along the pipes and radiators, and watch the pressure gauge for a slow fall, though a fill valve that tops the system up by itself can keep the gauge steady and hide a leak: why boiler pressure drops. For too little flow, Weil-McLain says to check that all the valves to and from the boiler are back at their proper setting.

What a technician does. Weil-McLain says a qualified technician de-limes the boiler if necessary, repairs the leaks and checks the pH, which should be between 7.0 and 8.5. It warns that in some cases the deposits are too heavy to remove.

Rushing water, whistling or humming

Water moving too fast. Honeywell says water noise at its zone valves can come from excessive water velocity. Grundfos’s fix for noise in the system when the flow is too high is to reduce the pump speed.

Pressure too low. Lochinvar lists low system water pressure among the causes of noisy operation, and says to verify the system is at a minimum of 12 psi. Grundfos says noise in the pump can come from too little inlet pressure, and says to check the air volume in the expansion tank, a technician’s job. Taco’s remedy for a 007e that is noisy from too little suction pressure is to raise the system pressure within its limits.

A pump humming through the house. Taco says to add vibration dampeners to the piping when a circulator is mounted to a wall or floor joists, to reduce noise traveling through them.

The burner itself. Lochinvar’s chart for a noisy Knight also lists a gas supply problem, a wrong gas and air mixture, and a dirty or damaged burner. Those are all technician jobs.

A bang when a zone valve closes

What it is. Water hammer: the moving water stops suddenly as a valve shuts. Weil-McLain recommends a pressure bypass valve on zone valve systems, to prevent too much flow through a single zone and water hammer when the valves close.

What you can do. Note which zone bangs and when, so the technician can find it quickly.

Ticking or creaking as the pipes warm

What it is. Pipes growing as they heat and rubbing on whatever holds them. Grundfos lists thermal expansion of system parts as a cause of noise in the system, and its fix is to check the pipe brackets and secure any loose ones.

What you can do. With the heat off and the pipes cool, look where the pipes pass through joists and brackets, and tighten anything loose.

Banging or clanking pipes and radiators

At the radiator. Castrads says a one-pipe steam radiator’s valve must be fully open or fully closed, because leaving it halfway open can cause very noisy steam hammer. Turn it with the boiler off and the radiator cold, and do not force one that will not move. Danfoss’s one-pipe steam instructions say free standing radiators must be properly pitched, so the water can drain back: the radiator should lean slightly down toward its valve, never toward the vent.

A big radiator that bangs halfway through a cycle. Peerless says a large radiator vented too quickly can hammer, and the fix is a smaller air vent, or two small vents with one higher than the other.

When it bangs tells the technician where to look. Peerless’s troubleshooting table lists these causes:

Wet steam. Burnham says wrong piping at the boiler sends wet steam into the system, and hammering is one of the problems that may follow.

The water level. Weil-McLain says normal is halfway up the gauge glass. Burnham says a steam boiler is surging when the water in the glass bounces or disappears while it makes steam, and Hydrolevel says foaming comes from oils, minerals and other dirt in the water. Peerless says an erratic water level with dirt in the glass means the boiler needs skimming. Those are jobs for a steam technician. If the glass shows no water at all, turn the boiler off and let it cool before any water goes in, because of the thermal shock Weil-McLain warns about.

Hissing or whistling radiator vents

A soft hiss as the radiator heats is normal. Castrads says the steam pushes the air out through the vent, which closes by itself when the radiator is full of steam.

A loud whistle as the radiator fills. DOE’s Building America steam report says a vent that whistles loudly as the radiator fills may have too small an opening, and should be replaced. It says a whistle can also mean dirt clogging the opening, or the boiler running at a higher pressure than it needs.

A vent that hisses steam or spits water. DOE says to replace any one-pipe steam vents that are clogged or stuck open. Danfoss’s list for a spitting vent is to check the radiator’s pitch, open the supply valve fully, check the riser air vent for the main system, and check for too much pressure.

Replace a vent with the boiler off and the radiator cold.