One of the most common issues in pianos is a sticky or sticking key. This problem could mean many different things as there are various things that could cause what we consider to be a sticking key. This article will go through some of the more common things that you would come across and that would be solutions to fixing a sticking key. It's also not just necessarily always one thing that is causing the problem. This article will walk you through the steps of checking the causes if you have a sticking key to figure out what the problem is. Here is a link to a video where we demonstrate many of these issues: Diagnosing the Sticking Piano Key
We are going to start at the front of the key. The first thing to check if it is a white key that is sticking is if the front of the key is too close to the key slip. It could be that the board that sits in front of the keys, which is called the key slip, is too close to the front of the keys. When you push the key down, it gets stuck if it is too close to the key slip. You can tell if you look down in between the front of the key and the key slip if you can see that there is no space there, then this is probably the cause of your sticking key. Another way to tell is if you pull back just a little bit on the key slip and the key comes up then you know that the key slip is too close. The way to fix this is to take the key slip off. In most cases there will be screws underneath the key slip that you remove and then the key slip will come off. Then what you do is put a shim on the keyframe so it will push out on the key slip a slight amount. You can just make a shim out of either a piece of thin cardboard or thick paper. You can tape it to the key frame to hold it in place. The shim doesn’t have to push the key slip out very much, just enough so that there is a little bit of space between the front of the key and the key slip.Often, I’ll just tear off a piece of one of my business cards because I usually have those with me when I’m working on a piano.Sometimes I have to double it up by folding it. Here is a link to a video which shows how to fix this issue: Fixing Sticking Piano Keys by Adjusting the Keyslip
Another possible cause of a sticking key is that the wood key stick may be warped causing a key to rub up against its neighbor which will cause additional friction so the key can’t return properly.
Another problem that could be causing the sticking key is the key bushing which is underneath the key and that sits on the key pins could be too tight on the pin. The pins in the middle of the key are the balance rail pins and the pins in the front of the key are the front rail pins.The bushing could be tight because it is felt and sometimes it swells with changes in humidity throughout the year. It may need to be replaced or eased. We have a video that shows replacing the front rail key bushings.It could also be that the balance rail felt is too tight. There is felt in this hole and it sits on the pins in the middle of the key which are the balance rail pins. If either of these two felts are too tight you can push down on the key and because it is too tight the key will not want to return up. You may need to replace the felt or just ease it. There are tools available to iron the felt to give it a better fit on the pin. Here is a link to a set of videos on how to replace the bushings: Piano Key Bushing Replacement
Another possibility is that the front rail pin or the balance rail pin is corroded. As you take the keys out you can feel if they are smooth. They may be rough because they have a little bit of corrosion on them. If they have a lot of corrosion you will have to replace the pins. In most cases you can just use some metal polish and polish these up so that they are nice and smooth so the key can move freely up and down on the pin. The same with the balance rail pins. If they are smooth you probably don't need to polish them.We offer a video demonstrating how to polish the key pins as well as lubricate the key bushings so they move more freely: Cleaning & Polishing Keypins
In most cases the front rail pins are oval shaped so the dimension side to side is not as wide as the dimension front to back. Sometimes if a key is too loose it wobbles side to side. Some technicians will take and turn that pin just a little bit so that it tightens it up, and over time can cause the key to be too tight. You want to make sure that it's not turned so that it makes the key too tight on the pin.You’ll also want to check to see if the pin is bent as this can cause the key to be too tight on the pin.
Coins and paperclips are common problems. They fall between the keys and get wedged in between them so it can't go down and won't come back up. You will want to check that by lifting off the key to see if there is anything lodged in between the keys.
A broken key stick is another possibility that will make the key not play properly. Sometimes you will see that there is a break and it's usually right at the balance rail in most cases. If there is a break in the key then the front will go down down but the back won't come up at the same time because the key is broken.
Other things that could cause a sticking key would take place in the action, including the whippens, the hammer butts, and the hammers. The whippen has a jack and a jack spring. If the jack spring is broken, the jack won’t be able to return properly which will make it so the note won’t play because the jack won’t be pushing up on the bottom of the hammer butt. In this case you will need to replace the jack spring. Piano Jack Spring Replacement
Another possibility is the jack flange. Sometimes it becomes unglued. You might be able to see that it's glued to the main whippen body and if that glue joint breaks the jack will be out of place causing a key to stick. I have seen this several times. It just pops off and then the jack won’t able to do its job, because it's not attached to the whippen. It's a simple job to put a dab of glue on the slot where the flange goes to put the jack back onto the whippen body.You will need to remove the action and the whippen in order to glue the flange back on.
Probably the most common cause of a sticking key is a tight jack flange.This is often times the problem if the note plays sometimes, but other times will seem to get stuck and won’t play. This is more common with the damper pedal down. You will keep hitting it and it won't keep playing and sometimes you can hit it a few times and it will go back to playing again but sporadically. The reason it doesn’t respond it that the pin in the jack flange is too tight. The pin that holds the jack to the flange goes through a hole with felt in it and the felt can swell and cause the pin to be too tight. This can also happen to the whippen flange or the hammer flange.These problems can occur especially in the summertime or certain times of the year when the humidity is higher. To fix this problem you will need to measure the flange with a gram gauge and it should have anywhere from one to four grams of resistance on it. Possibly one to three grams.You won’t want it to be so loose that it wobbles back and forth because that will cause other problems. You want it to be loose enough so that it will return to its position. If it’s too tight the jack will come forward, but it won’t make it all the way back underneath the hammer butt which will make it so that the note won’t play. It won’t play because it won’t be pushing up on the bottom of the hammer butt. Sometimes you can simply put some Protek CLP on the flange pin and that will be enough to correct it. If it’s severe you will need to take the whippen out and repin the flange which I show in a video. This will correct the tightness to the right resistance level. Fixing a Sticking Jack
A tight flange can also occur on the hammer flange.This will be evident if the hammer doesn’t return as quickly as it should.This can be measured also with a gram gauge and is fixed the same way as the jack flange. Piano Flange Repinning
Another problem that may cause the jack to not return properly is if the lost motion is not adjusted to the proper level.If this adjustment is set too high so that there is what we call negative lost motion, then the jack may not be able to reset properly.We have a video which addresses this problem. Adjusting Lost Motion in a Vertical Piano
Another possible cause of a sticking key is a broken bridle strap. This is common in older pianos and can make it so that the hammer or whippen won’t return and pull the hammer butt back into position quickly enough.If this is the case, you just need to replace the straps. Piano Bridle Strap Replacement
You can also look to see if you have a broken hammer shank. This would obviously make it so that the hammer doesn’t work correctly as it may have fallen inside the piano.
Another type of flange that could be broken is the hammer flange. If the hammer flange is broken it will not hold the hammer in place and it will wobble back and forth.
You should also check the hammer rail spring to see if it is broken or out of place.There are a couple of different types of hammer spring out there. Some are attached to a rail and the spring pushes up against a slot in the hammer butt.If this spring is broken, which happens occasionally, or it could just be out of place, then the hammer is not going to have enough spring to return it to its position. If this happens you either replace or reposition the spring as these springs can become weak over the years. Piano Hammer Butt Spring Replacement
If it’s on a spinet piano, because the keys are shorter, the whole action is dropped down inside the piano below the level of the backs of the keys. There is usually an elbow that attaches to the bottom of the whippen and a lifter wire that comes up to attach to the back of the key.That elbow can be broken, so if you have a key that is in the down position and it doesn’t stay up on its own and it’s a spinet piano there is a good chance that it has a broken elbow. You can easily replace a plastic elbow and we have them available for purchase in our online store. If you continue to look further, you may find that the lifter wire on the back of the key has become disconnected. You will need to reconnect it.
This is just a partial list of things that could cause a sticking piano key, but from my experience they are some of the most common causes.