How to Buy Genuine Used Siemens Industrial Automation Parts

A cheap Siemens PLC is only a good deal if it is genuine, correctly identified, properly tested, and suitable for your application.

Industrial automation equipment is not something you want to gamble on.

A failed PLC, HMI, communication module, or drive can bring an entire machine or production line to a standstill. When an original component is obsolete or difficult to source, buying used or surplus Siemens automation parts can be a practical way to restore equipment while controlling replacement costs.

But there is a problem:

Not every product advertised as “genuine Siemens” is necessarily what the buyer expects.

Used, surplus, refurbished, repaired, obsolete, and counterfeit products can look very similar in online listings.

So how do you buy used Siemens industrial automation parts with confidence?

This guide explains what to check before purchasing used Siemens PLCs, HMIs, drives, CPUs, I/O modules, communication modules, power supplies and other Siemens automation equipment.

Why Buy Used Siemens Automation Parts?

Siemens industrial automation equipment can remain in service for many years.

A factory may still be operating a machine built around an older Siemens S7-300 or S7-400 system even when newer PLC platforms are available.

Replacing the entire control system may require:

New hardware
New programming
Engineering time
Machine modifications
Testing and commissioning
Production downtime
Significant investment

In some situations, replacing one failed module with a compatible used or surplus unit can be much faster and more economical.

This is particularly important when a machine contains an obsolete or discontinued Siemens component.

Siemens itself provides spare-parts and lifecycle services because industrial equipment can reach the point where replacement parts are needed to prevent extended downtime.

The key is not simply buying “used.”

The goal is buying the right part, from the right source, in the right condition.

1. Start With the Exact Siemens Part Number

This is the first and most important step.

Do not buy a Siemens PLC simply because the product name looks correct.

Siemens has many visually similar products with different technical specifications, firmware versions, communication interfaces, memory configurations, voltage ratings and hardware revisions.

For example, two products may both be described as an:

Siemens S7-300 CPU

but have completely different order numbers.

Always ask for:

Complete Siemens order number
Product/model number
Hardware version
Serial number, where applicable
Firmware version, where relevant
Product photos
Nameplate photos
Connector/interface photos

The complete order number is much more useful than a generic description such as “Siemens S7-300 CPU.”

Siemens documentation also uses product and serial numbers to identify equipment and locate appropriate spare parts.

Pro tip

Send the supplier a photo of your existing part.

If possible, provide:

Part number + photo of nameplate + quantity required + application

This reduces the chance of ordering the wrong variant.

2. Understand the Difference Between Used, Surplus and Refurbished

One of the biggest mistakes buyers make is assuming these words mean the same thing.

They don't.

Used

A previously installed product that has been removed from service.

It may be fully functional, partially functional, untested, or faulty.

Surplus

A product that is excess inventory or no longer required by the previous owner.

Surplus equipment may be:

New old stock
Open box
Unused
Previously stored
Previously installed

The exact condition must be confirmed.

Refurbished

A previously used product that has undergone some level of inspection, repair, restoration or testing.

However, “refurbished” does not automatically mean refurbished by Siemens.

Siemens' own refurbished products undergo a defined refurbishment and testing process and are restored to the original technical specifications and performance characteristics.

Therefore, when a supplier says:

“Siemens refurbished”

ask:

“Refurbished by whom?”

That single question can prevent a lot of confusion.

3. Ask for Real Photos, Not Catalogue Images

This is one of the easiest ways to filter suppliers.

If you are buying a used Siemens PLC, ask the seller for actual photos of the exact unit being supplied.

Don't rely only on a Siemens catalogue photograph.

Ask for photographs showing:

Front

Check:

Siemens branding
Model identification
LEDs
Connectors
Physical condition
Scratches or damage

Side and rear

Check:

Labels
Connectors
Mounting points
Housing condition
Signs of modification

Nameplate

The nameplate should clearly show relevant identification information.

Serial/identification markings

Where applicable, compare the information shown by the supplier with the product documentation and purchase records.

4. Check the Part Number Carefully

A single character can make a major difference.

For example, Siemens order numbers can contain detailed information about:

Product family
CPU type
Communication interface
Memory
Voltage
Hardware revision
Product configuration

Never assume that a visually similar replacement will work.

Before placing the order:

Copy the exact part number from your machine and send it to the supplier.

Then ask:

“Please confirm that the supplied unit is exactly this part number and provide a photograph of the nameplate.”

Get the confirmation in writing.

5. Ask How the Unit Was Tested

This is where many cheap deals fall apart.

A supplier saying:

“100% tested”

is not enough.

Ask what was tested.

For a PLC CPU, testing may involve appropriate power-up and functional checks, communication checks, diagnostics, and application-specific testing where feasible.

For an HMI, you may want to know whether the display, touchscreen, communication ports and power-up operation were checked.

For a drive, ask whether the unit has been tested for appropriate power-up, display/keypad operation, fault status and relevant functions.

The exact testing procedure will depend on the product.

Ask the supplier:

“Can you provide a test report or test video for this unit?”

A serious supplier should be able to explain the testing process clearly.

6. Check for Signs of Repair or Modification

Used industrial electronics can sometimes be repaired or modified during their previous life.

Look carefully for:

Broken seals
Missing screws
Damaged housings
Reworked circuit boards
Unusual soldering
Burn marks
Corrosion
Damaged connectors
Missing labels
Heavy cleaning or repainting
Mismatched labels

This doesn't automatically mean the product is bad.

A professionally repaired unit may still be useful.

The important thing is knowing what you are actually buying.

Siemens documentation also notes that certain authenticity/security labels are designed to indicate whether a component has been manipulated. Where such a label exists, a damaged label can be an important warning sign.

7. Don't Confuse Cosmetic Condition With Functional Condition

A used PLC may have:

Scratches
Faded labels
Minor discoloration
Stickers
Signs of previous installation

That doesn't necessarily mean it is defective.

Conversely, a product that looks almost new is not automatically genuine or functional.

Appearance is evidence of condition, not proof of functionality.

This is why testing matters.

Siemens' own refurbishment process distinguishes cosmetic restoration from functional testing and releases refurbished products only after they pass the applicable functional and quality tests.

8. Ask About Warranty and DOA Policy

Before buying a used Siemens automation component, ask:

What happens if the product doesn't work?

A proper supplier should clearly explain:

Warranty period
DOA policy
Return conditions
Testing requirements
Replacement policy
Refund policy

Don't wait until after delivery to discover that the seller considers every used product:

“Sold as is.”

For critical automation components, warranty terms can be just as important as the purchase price.

9. Check the Supplier, Not Just the Product

A genuine-looking Siemens PLC from an unknown seller is still a risk.

Look at the supplier's:

Business history
Company website
Physical address
Product inventory
Customer reviews
Industry experience
Return policy
Warranty policy
Product photographs
Communication quality

Ask yourself:

Can I find this company again if there is a problem?

Siemens itself warns that products sourced through unknown or grey-market channels can carry risks including lack of expected support or warranty and the possibility of receiving used, damaged, non-functional or counterfeit products.

10. Don't Choose the Cheapest Supplier Automatically

This is where procurement teams often make a costly mistake.

Imagine you receive three quotations:

Supplier	Price	Testing	Warranty
Supplier A	₹18,000	Unknown	None
Supplier B	₹21,000	Tested	30 days
Supplier C	₹24,000	Tested + documented	90 days

Supplier A looks cheapest.

But if the PLC fails after installation and causes several hours of machine downtime, that ₹3,000 or ₹6,000 saving can become meaningless.

Think about total cost, not purchase price.

Cheap hardware + machine downtime = expensive mistake.

11. Be Especially Careful With Obsolete Siemens Parts

Older Siemens automation systems can be difficult to replace with new equipment.

This creates demand for:

Used Siemens PLCs
Surplus Siemens modules
Obsolete Siemens CPUs
Used Siemens HMIs
Siemens communication modules
Siemens I/O modules
Siemens power supplies
Used Siemens drives

For these products, finding the correct original part number is critical.

If your machine depends on an obsolete component, replacing it with the wrong variant can create additional engineering work and downtime.

12. Ask for a Part Number Before Asking for a Price

Instead of sending:

“I need a Siemens PLC. What is the price?”

send:

“I need Siemens 6ES7 XXXXXXX, quantity 2. Please quote your best price and confirm condition, testing status, warranty and availability.”

This immediately makes your inquiry more professional.

It also makes it easier for suppliers to provide an accurate quotation.

13. Use a Simple Buyer Checklist

Before purchasing any used Siemens automation part, check these 10 points:

Used Siemens PLC Buyer Checklist

☐ Exact part number confirmed
☐ Actual product photos received
☐ Nameplate checked
☐ Serial/identification information reviewed
☐ Condition clearly stated
☐ Used/surplus/refurbished status confirmed
☐ Testing procedure explained
☐ Warranty confirmed
☐ Return/DOA policy confirmed
☐ Supplier identity and reputation checked

If several boxes remain unchecked, don't rush the purchase.

Can Used Siemens Automation Parts Be a Good Buy?

Absolutely.

Used and surplus industrial automation equipment can make sense when you need to:

Repair an existing machine
Replace an obsolete component
Reduce replacement costs
Maintain legacy equipment
Minimize production downtime
Keep an older automation system running

But the quality of the purchase depends heavily on identification, condition, testing and supplier reliability.

The objective isn't to find the cheapest Siemens PLC.

The objective is to find the right Siemens PLC that actually works.

Where Can You Buy Used Siemens Automation Parts?

There are several ways to source Siemens automation equipment:

1. Authorized Siemens channels

Best suited when you need new equipment, official support and manufacturer-backed purchasing.

2. Manufacturer-refurbished equipment

Siemens offers refurbished automation products that have gone through its own refurbishment and testing processes.

3. Industrial surplus suppliers

These suppliers may have discontinued, surplus or used Siemens products that are difficult to source through conventional channels.

4. Specialized automation parts suppliers

Specialized suppliers can be useful when you need a specific obsolete PLC, HMI, drive or module quickly.

Looking for a Used Siemens PLC or Automation Part?

At PLC HUB, we help businesses source new, used and surplus industrial automation equipment, including Siemens PLCs, CPUs, I/O modules, HMIs, drives and other automation components.

If you already know the part number, you don't need to search through hundreds of products.

Send us the Siemens part number.

We can check availability and provide a quotation based on the required product and condition.

Need a Siemens part?

Send Part Number → Get a Quote

Final Thoughts

Buying used Siemens industrial automation parts doesn't have to be risky.

The biggest mistake is treating a used PLC like an ordinary electronic component.

It's part of a machine's control system.

Take the time to verify the part number, product condition, authenticity indicators, testing, warranty and supplier before you buy.

And remember:

The cheapest PLC isn't necessarily the cheapest solution. The right PLC is the one that gets your machine running reliably.

For critical equipment, always verify compatibility against the applicable Siemens documentation and your machine's engineering requirements before installation.

About PLC HUB

PLC HUB supplies industrial automation components for businesses looking for new, used and surplus automation equipment.

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