Slot Machine Malfunctions

When players don't get the jackpot money they expected

Last update: November 8, 2024

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Like all machines, slot machines occasionally screw up.  And the most annoying screwup is when they tell you that you won, when you actually didn't.  We'll cover how and why that happens, along with every single case I could find and whether the player eventually got paid or not (usually no, but sometimes yes).  And as usual, Easy Vegas is the only website on the entire planet that has this kind of information.

Kinds of malfunctions

There are three main types of malfunctions that make players think they won: 

1. Display errors.  A video slot shows a huge number of credits won, even though the player didn't land the jackpot symbols on the payline.
2. Setting errors.  The player lines up a winning combo, but the machine is set to the wrong jackpot amount.
3. Mechanical errors.  On slots with physical reels (i.e., not video slots), the reels can accidentally land on a winning combo even though that's not what the computer actually chose.

There are many examples of each, and I cover all of them.

Display errors

Sometimes slot machines show an impossibly large number of credits won.  And I do mean impossibly large: the number of credits shown as won is way larger than the actual top jackpot on the machine.  (It might say you won $56 million when the most it's even possible to win is only $99,000, according to the paytable that the machine shows.)  In most cases of a display error, the players didn't even line up the symbols in a winning combination for the top prize.  Cases like this are simply programming errors.

Some players might wonder, “If these display errors happen, how can I trust the game at all?  How do I know that it's not ripping me off all the time?”  That's a fair question.  The answer is that the random number generator (RNG), the heart of the machine, is completely separate from the part that controls how many credits are displayed.  The RNG is also subjected to rigorous testing by the game manufacturer, and, in many cases, by the governmental agency that regulates gameplay in whatever jurisdiction the game operates.  Further, both the casino and the agency can run diagnostics on demand to test the RNG and other aspects of the game.  In short, the occasional display error doesn’t suggest that the overall game itself is faulty.

Mechanical Errors

With video slots, the common malfunction is that the machine shows a bunch of credits won, even when the player didn't line up the jackpot symbols.  With electro-mechanical (physical-reel) slots it’s the opposite: the jackpot symbols line up, but the machine says the player won nothing, or just a small amount.  In these cases, the computer inside the machine has chosen the correct combination to be displayed, but for whatever reason, the physical reels don't actually display what the computer chose.

The reason this happens is because of a "tilt".  There are two kinds of them:

1. Hopper tilt.  The hopper is the bill acceptor.  The machine can go into hopper tilt when the acceptor gets jammed, or the machine thinks someone is trying to open the cash door.
2. Reel tilt.  If the machine detects something wrong with the spinning mechanism of any of the reels (that could cause a reel to land on a different symbol chosen by the random number generator), the machine goes into reel tilt.

When a tilt happens, the reels will either stop immediately (rather than stopping on the combination the computer chose), or spin backwards until the error is cleared, where again, they'll stop suddenly, and not on the combo chosen by the computer.  When the reels stop suddenly, it's possible that the jackpot symbols might happen to all land on the payline.  But if so, that's just a side effect of the sudden shutdown; the reels didn't stop where they were supposed to stop.

To be clear, the design of the tilt condition is often super sloppy.  The reels might actually stop (instead of spinning continuously), the game doesn't power down all the lights, and in games that have a physical wheel and a video screen (e.g., Wheel of Fortune), the error message does not unambiguously tell the player that there’s been a malfunction and the player didn’t win.

Should the player get paid?

When a slot malfunctions, players don't get—and don't deserve—the big payout.  If a blackjack dealer accidentally said you won $5000 when you actually won only $500, you wouldn't insist that you won just because the dealer misspoke.  You wouldn't jump up and down screaming, "But you said!  You said!  I'm gonna sue!"  You wouldn't do that unless you were a complete idiot.  But as soon as a machine makes the same kind of error, misstating that a player won when she obviously didn't, then players suddenly become completely irrational.

A display error on a slot machine is just the machine version of a dealer misstating the payout.

On the other hand, casinos and slot makers often do have some culpability.  Casino staff often open the machine and screw around with it before the Gaming Commission gets onsite to investigate, spoiling the evidence.  A court ruled in favor of a player at least once for this very reason.  (Of course, that argument usually loses, because the casino's failure to call Gaming is between the casino and Gaming, not between the casino and the player.)  And slot makers don't design the machines to make it obvious to the player that a malfunction has occurred, so it's their fault that players keep thinking they won jackpots when they actually didn't.

Myth:  “Machines never seem to glitch when players lose, only when they [seemingly] hit a jackpot.”

Wrong.  Glitches happen all the time, even when the amount won (or lost) is trivial.  The reason you don't hear about those cases is, why would you?  Can you imagine this headline in the news?

“Slot player's machine froze after landing on a non-winning combination.”

In cases like that, nobody cares.  It makes the news only if it's a supposed jackpot that doesn't actually get paid.  Then everyone hears about it.  Otherwise, you don't.

Years ago I played a slot, hit for a small win, but the machine seemed to pay a little more than I thought I'd won.  I flagged down a slot attendant and asked about it.  He couldn't figure it out, so he called another attendant, and he couldn't figure it out either.  We didn't pursue it, and that was the end of it.  I certainly didn't alert the media.

Also, if a slot thinks the cash box is being breached, or it detects a mechanical problem on a machine with physical reels, it's gonna lock up, whether the payline shows a winning combination or not.  The media gets called only when the machine locked up on an otherwise winning combo.

And guess what?  Once a player legitimately won a $229k jackpot in Vegas, but because of a malfunction, the slot machine didn't tell him. (CBC)  The casino alerted the Gaming Commission who spent considerable effort tracking down the player who had already returned to his home state of Arizona.  Most of the stories on this page are about players who didn't legitimately win a jackpot even though they want to believe that they did, but this case is the opposite: the player actually won a jackpot but didn't know it, and between the casino and the commission, they made sure the player got paid.

(About that malfunction: the reporting on this case was typically sloppy, but from clues in various articles, it seems the machine was a wide progressive—sharing the same jackpot with other machines in NV—so the computer that determines whether a spin was a winner wasn't in the machine, but rather in the offices of the slot maker, and the slot maker's server couldn't communicate with the slot, so the server couldn't tell the slot that the player had won.)

One solution:  Slot Machine Warranties

Two simple changes could prevent malfunctions, or at least misleading malfunctions.

First, slot makers should warranty that their machines will operate properly, just like with any other product that can be purchased.  If the machine malfunctions and causes the player to think she won big, the slot maker should be required to make a substantial payout to the player (and to the casino also, if the player sues the casino).  Realize that in malfunction cases, casinos are just as much victims as the players:  They bought or rented a machine that somebody else made, it didn't work properly, and now they not only have an unhappy customer, but that customer is also probably suing them, over something that's in no way their fault.

A warranty would ensure that players get a decent amount of compensation for their bad experience, the innocent casinos would be off the hook, and slot makers would have an incentive to improve their machines so they don't keep screwing up.  State gaming commissions ought to mandate this kind of warranty, and until that happens, casinos should push slot makers to offer it even in the absence of regulation.  (A nod to Mission146 at the WizardOfVegas forum who first identified a warranty as way to combat slot malfunctions.)

Another solution:  Design the machines better

Slot makers could do a lot more to both prevent malfunctions and to make it obvious to players that a malfunction has occurred,  so that the players don't think they won and then call the media and sue the casino.

Let’s take display errors, where a video slot says the player won an impossibly large amount, way more than the top jackpot on the machine.  Just a few lines of code could prevent most to all of these.  Here's some sample pseudocode, which tells the machine to stop and show an error message if the amount won or accumulated is 1.5 times the top jackpot on the machine:

if (gameWin > topJackpot * 1.5) showErrorMessage
if (creditMeter > topJackpot * 1.5) showErrorMessage
if (ticketAmount > topJackpot * 1.5) showErrorMessage

In the case of mechanical slots with physical reels, where the reels sometimes improperly show a winning combo, there are a number of safeguards.  If the controller can't communicate with the reels:

1. Don’t just have the reel stop anywhere.  That's foolish.  Have the reel spin continuously (preferably backwards) until a slot tech resets the machine.
2. Power down all lights on the machine, except for the error message.
3. Have the error message address the player.  Most error messages are written with a slot tech as its audience, in terms that mean nothing to a player.  The message when the game controller couldn’t communicate with the Wheel of Fortune bonus wheel is, ridiculously, "REEL TILT:  REEL COULD NOT FIND STOP.  Single Wheel, Reel 1.  PLEASE CORRECT THE ERROR AND TURN THE RESET KEY.") (6 ABC Philly video)  A proper message would be something like:
   
   We’re very sorry, but there has been a malfunction.  Please call a slot attendant.  You will be paid any winnings which are due (which might be different from what the game displays, because the game might have stopped on the wrong symbols).  If the casino can’t determine whether your spin was a win, you will be refunded the price of the spin.
4. Slot tilt messages often tell the slot attendant to reset the machine, as per above.  (“PLEASE CORRECT THE ERROR AND TURN THE KEY.”  This is significant:  The slot maker is directing the casino to spoil the evidence!  Instead, below the proper message to show to the player (above), or on the next screen, the machine should say something like:
   
   Slot Attendant:  Reel tilt.  Could not find the proper stop on this reel:  Bonus Wheel.  If the game appears to show a winning combination, and the player thinks s/he has won, DO NOT OPEN THE MACHINE.  Call the Gaming Commission.  Otherwise, if there is no payout in dispute, then turn the reset key to reset the machine.
5. If there’s a temporary power failure, which could cause the reels to stop on a jackpot combo, just put a tiny battery in the machine to make sure the reels can move to a stop other than the jackpot.

All the cases

Play slots online

I suggest you play something other than slots because slot odds are so bad.  You could also play online with fake money, because then it doesn't matter if you lose.  A good casino for free-play is Bovada, since it requires no download and no registration.  (If you see a registration box, you can close it and continue without registering.)  You can play with real money too, though I hope you won't (or at least won't bet more than you can comfortably afford to lose). (advertisement)

All my slot machine articles

• Slot machine basics.  How much it costs to play, how much you can win, expected loss, why they're a bad bet, why they're popular, how you can limit your losses, speed of play
• How to play slot machines
• Slot returns.  How much they pay back.
• The Randomness Principle.  Slots don't continually get looser and tighter as they're played.  They don't have to.
• How they work. Explains the randomness principle, and runs through the math to show how a game returns a particular payback percentage.  There's a companion page on Par sheets.
• Strategies. Tips for increasing your chances of winning, and saving money.
• Slot Jackpots.  Odds of hitting the jackpot, progressive jackpots, and other jackpot topics.
• Bonus Rounds (all about them)
• How to Beat Slot Machines, aka Advantage Play (AP).  It's not what you think: it's not easy, and for the most part, not lucrative.
• Slot Machine malfunctions. How and why slot machines screw up, causing players to think they've won the jackpot when they really haven't.
• Slot Machine Myths
• Slot Machine B.S.  Wrong info that's published elsewhere.
• Biggest Jackpots.  The largest slot and table game jackpot wins in Vegas.
• Skill-Based Slots.  The scoop on the new games in which your results aren't entirely determined by chance.
• Slot Machine Simulator.  I programmed an exact replica of the Blazing 7s slot (odds-wise).  Click it to play thousands of spins in one second and see how you do.
• Slot name Generator.  Randomly creates a slot machine name using common slot words.  Hilarious!