Steam Radiators Make a Popping Noise. What To Do?

A visitor to the Wall asks, "I'm getting expansion noises from a cast-iron radiator and trying to figure out where it coming from."

"Maybe the pipe that comes through the floor is hitting wood? Or could it be coming from parts of the radiators? It's not terrible we're light sleepers and when the heat is coming up, it pops and ticks enough to wake us both up. Any ideas on what to do, or is it a part of steam heat that you accept?"

A member of the community comments:

It could be either, but usually, if it's the radiator, you'll hear a 'ping!' caused by the vibration of the truss rods that hold the radiator sections together, unless someone has gobbed so much paint on the radiator that they can't vibrate. When a pipe is rubbing against wood it makes more of a 'clack-clack' sound or a dull knocking sound, but it doesn't sound metallic unless the movement is close enough to the radiator to transfer some of the force of the movement to the radiator.

To isolate the source of the noise, check and see if it is happening while the radiator is warming, or just before. You can also use a welder's glove or oven mitt to feel different parts of the radiator and see if you can deaden the noise by applying pressure with your hand. If the noise is coming from the pipes moving against wood, you can sometimes quiet the noise by dusting the area with talcum powder (real talc, not the corn starch baby powder) and brushing and blowing it into the gaps, but this only works temporarily. If you can work some PTFE thread seal tape in between the pipe and the wood it will last a little longer.

Another approach is to use high-temp silicone sealant to seal the area of penetration and deaden any movement. If the noise is coming from the radiator, it's not going to be easy to fix. Most radiators have their sections connected by tapered push nipples that form an opposition fit when the sections are drawn together by the truss rods. If the truss rods aren't tight enough, or if the tension isn't uniform, the push nipples can back out of their sockets when they expand, pushing the sections apart slightly, until the tension of the truss rods keeps them from going any farther.

I haven't done this yet, but I suspect what's necessary is to take the radiator apart, replace any worn push nipples (or maybe replace them all to be on the safe side), put it back together and torque the truss rods. I don't even know where to find the torque specifications yet or if they are even available, but if all else fails, I can compare them to some of my other radiators that aren't making noise. You can tell when two rods of equal length are at the same tension by the sound they make, and tension is actually more important than torque.

And another member has this to add: 

Expansion noises can be extremely difficult to find, never mind fix. The suggestion to see when the noise occurs in relation to when steam hits the radiator is excellent, and should help you locate where they are coming from. If they are in the feed pipe, make sure that the pipe isn't touching wood anywhere (if it is, try slipping a piece of plastic milk bottle in there -- it sometimes helps). This doesn't always do it, though, as sometimes the noise is in the pipe itself, as it moves and the threaded joints give a little (which they should).

If it is in the radiator itself, check how the feet of the radiator meet on the floor. Try the plastic milk bottle trick again. However, if it is from slight movement between the sections of the radiator, about all I can say is good luck.

If you should be inclined to take the radiator apart, or adjust the tension in the tie rods (if it has them -- not all do), work very carefully. This is not an easy job. On the tie rods, refrain from torquing them up too tight -- just tight enough so they don't rattle when the radiator is cold is ample (on clean threads, finger tight plus a half turn). It is dismayingly easy to break them, or strip the threads, and dismayingly difficult to get replacement parts. They are NOT made to pull the radiator sections together -- just to keep them from creeping apart with time. To pull the sections together on reassembly, use a pair of pipe clamps and tap (don't bang!) the sections as you pull them up with the clamps evenly.

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