Card machine not working? Work through these five causes, in order
Last updated: August 2026 · Rates checked: August 2026
Quick answer:five causes explain almost every dead card machine, and you can check each in about two minutes. In order of likelihood: (1) lost connection, so test the wifi on another device or check the signal bars on a SIM terminal and restart both router and terminal; (2) power, so charge it for ten minutes and hold the power button for a full restart; (3) a provider or acquirer outage, which looks like every card declining at once, so check your provider’s status page; (4) a hardware fault, which is what is left when the problem survives a restart on a good connection; (5) an account suspension, where the terminal works but everything declines, so call the number on your terminal or statement.
A card machine never fails at a quiet moment. It fails with a queue at the till and a customer holding a card in mid-air. The temptation is to phone your provider immediately, but the two most common causes, connection and power, are things you can fix yourself faster than you can get through a call queue. So work down this list in order: each step takes about two minutes, and the order reflects how often each cause turns out to be the culprit.
| # | Cause | The 2-minute check |
|---|---|---|
| 1 | Lost connection (wifi or SIM signal) | Can other devices use the same wifi? Does the terminal show signal bars? Restart router and terminal. |
| 2 | Power or battery problem | Put it on charge for 10 minutes, then hold the power button for a full restart. |
| 3 | Provider or acquirer outage | Every card declining at once? Check your provider’s status page or app. |
| 4 | Terminal hardware fault | Fault survives a restart, on a known-good connection, with full battery? It is the hardware. |
| 5 | Account suspension or hold | Terminal works but payments decline, or you have an email from your provider? Call them. |
1. It has lost its connection
Every card machine needs a live data connection to authorise payments, whether over wifi, a SIM, or an ethernet cable on a countertop unit. Connection loss is the most common cause of a “broken” terminal, and it usually looks like payments timing out or a connection error on screen rather than a dead device.
The check: if the terminal uses wifi, test the same network on your phone. If the wifi is down for everything, restart the router and wait two minutes. If the wifi works elsewhere but not on the terminal, restart the terminal and, if it lets you, forget and rejoin the network. If the terminal uses a SIM, look at the signal indicator; a portable terminal that works by the till but fails at the far end of the building or in a courtyard is almost certainly dropping signal, not breaking. Moving a few metres, or switching the terminal to a phone hotspot if it supports wifi, settles the question quickly.
If it keeps happening: a terminal that drops connection every busy Friday is not fixed, it is waiting. Persistent signal problems are worth raising with your provider, because some terminals can fall back between wifi and mobile data and some cannot, and that difference is invisible on a sales brochure and very visible in a queue.
2. Power and battery
Portable terminals live hard lives: dropped, left off the dock, charged on frayed cables. A battery that no longer holds charge shows up as a terminal that dies mid-shift or reboots when you pick it up off the dock.
The check:put the terminal on its charger or dock for ten minutes, make sure the charging light actually comes on (dirty dock contacts are a classic), then hold the power button down for a full restart. A surprising number of “dead” terminals come back at this point. If the charging light never comes on, try a different cable or socket before declaring the terminal faulty.
3. Is it you or them? Spotting a provider outage
Sometimes your kit is fine and the problem is upstream: your payment provider, their acquirer, or occasionally a card scheme is having an incident. You cannot fix this from your shop floor, but you can diagnose it fast, and knowing it is them changes what you do next.
An outage has a distinctive shape. Every card starts declining or timing out at once, across different customers, banks and card types. One declined card is a customer problem; ten in a row is not. The terminal itself often looks healthy, connected and charged, and simply fails at the authorisation step.
The check:look at your provider’s status page (search the provider name plus “status”, or open their app if you have one), and if nothing is posted, call the support number printed on your terminal or statement. If a nearby business uses the same provider, ask them; an outage shared is an outage confirmed. During a genuine outage, note the failed transactions so you can reconcile later, and either take cash, send payment links from another device if your provider supports them, or fall back to a backup reader on a different provider, which is the one option that keeps cards working no matter whose infrastructure has fallen over.
4. The terminal itself is faulty
Hardware faults are what remain when you have eliminated everything else: the connection is proven good, the battery is charged, no outage is reported, and the terminal still misbehaves. Typical symptoms include a card reader that no longer reads chips or contactless taps, a screen or keypad that has stopped responding, or a terminal that crashes and reboots repeatedly even after a full restart.
Your rights:if you rent the terminal, it remains the provider’s property, and rental agreements generally include maintenance and replacement of faulty hardware. When you call, ask three things directly: is this covered under my rental agreement, what is the replacement timescale, and is there any charge for the swap-out. The exact service level is contract-specific, so have your agreement to hand, and if the answer to “how long” is vague, push for a date in writing. If you bought the terminal outright, your route is the manufacturer’s warranty plus your consumer or business purchase rights against the seller, and a pay-as-you-go provider will typically replace a reader that fails within its warranty period.
Worth logging: keep a note of each failure, with dates. If you later dispute a rental charge for a terminal that spent a fortnight broken, or want out of the contract, a dated log beats a vague recollection every time.
5. Your account has been suspended or held
The rarest cause, and the most serious. The terminal connects, the battery is fine, there is no outage, and yet every payment declines, or the terminal reports it cannot log in to your account. Providers can suspend processing while they run a risk review, chase missing documents, or investigate unusual transaction patterns, and the first sign is sometimes an email you have not read yet.
The check: search your inbox, including spam, for anything from your provider, then call them and ask plainly whether there is a restriction on the account and what they need from you to lift it. If money from recent takings has also stopped arriving, that points the same way; our guide to card takings not reaching your bank covers the difference between a settlement delay and a genuine hold, and exactly what to ask on that call.
What downtime actually costs
Here is the arithmetic that makes a backup reader the cheapest insurance in your business. Suppose your terminal dies on a Saturday and £600 of card takings walk out of the door, customers who could not pay and did not come back. That £600 is gone. Compare the cost of having had a pay-as-you-go backup in the drawer: a Square Reader is £19 + VAT one-off and a SumUp Solo is £29 + VAT on current pricing, with no monthly fees on either. Putting the £600 through the backup instead costs you only the flat transaction rate: at SumUp’s 1.69% that is £600 × 1.69% = £10.14, and at Square or Zettle’s 1.75% it is £600 × 1.75% = £10.50. So the choice on the day is lose £600, or keep roughly £589.50 of it. Even counting the £19-£29 purchase, the reader pays for itself many times over the first day it is needed, and it costs nothing to own in the months it sits in the drawer.
Keep a backup reader. Genuinely.
This is not a sales line; it is the single most useful thing to take from this page. A backup on a differentprovider from your main terminal protects you against every cause on this list at once: your provider’s outage does not touch it, your terminal’s hardware fault does not touch it, and even an account hold on your main provider does not touch it. Set it up on a quiet day, not during the emergency: the account approval, app login and a £1 test transaction all want doing while nothing is on fire. Our rates comparison shows the current pay-as-you-go options side by side.
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If this keeps happening, this is why merchants leave
One failure is bad luck. A pattern of failures is a provider problem, and it is one of the most common reasons businesses switch: not the rate, but the fourth Saturday spent on hold to a support line while the queue melts away. When you compare providers, ask the questions this page has taught you to ask: how fast is support actually answered, what is the terminal replacement timescale in writing, and can the terminal fail over between wifi and mobile data. If you are mid-contract, exit fees are not always the wall they appear to be; our guide to getting out of a card machine contract works through the options, and our cancellation guides for Worldpay, Barclaycard and Elavon cover the mechanics provider by provider.
Frequently asked questions
Why has my card machine suddenly stopped working?
In rough order of likelihood: it has lost its internet connection (wifi drop or weak SIM signal), it has a power or battery problem, your payment provider or their acquirer is having an outage, the terminal itself has developed a hardware fault, or your merchant account has been suspended. The first two are fixable on the spot in a couple of minutes, which is why you always check them before phoning anyone.
How do I know if my card machine provider is down?
Three quick signals. First, every card starts declining or timing out at once, across different customers and card types, which one dodgy card cannot explain. Second, your provider’s status page (search the provider name plus "status", or check the app if they have one) shows an incident. Third, other businesses nearby on the same provider are having the same problem. If all three line up, it is them, not you; keep your receipts of the failed attempts and wait it out or fall back to a backup reader.
Can I get a replacement if my rented terminal is faulty?
Usually yes. Terminal rental agreements generally include maintenance and replacement of faulty hardware, because the terminal remains the provider’s property. Check your contract for the service level: what counts as a fault, how quickly a swap-out is dispatched, and whether next-day replacement costs extra. If your provider cannot tell you a replacement timescale on the phone, that in itself tells you something about the support you are paying for.
Should I keep a backup card machine?
If losing a day of card sales would hurt, yes. A pay-as-you-go reader costs £19-£29 + VAT one-off (Square Reader £19, SumUp Solo £29 on current pricing), has no monthly fee, and only costs you its flat rate (1.69%-1.75%) on transactions you actually put through it. One saved £600 Saturday pays for it roughly twenty times over.
Related reading
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