Why S5 Migration Can't Wait Until 2027

Every Siemens S5 PLC running today is an unplanned downtime event waiting to happen. Siemens ended all S5 support on September 30, 2020. No spare parts from the manufacturer. No repairs. No technical support. The longer you delay migration, the more expensive and risky it becomes. Here is why 2026 is the year to act — not 2027, not 2028.

The S5 Spare Parts Crisis Is Getting Worse Every Month#

Since October 1, 2020, the only source for S5 replacement parts is the third-party refurbished market. Companies like ClassicAutomation, Northern Industrial, Foxmere, and various eBay sellers offer refurbished S5 modules with 12–24 month warranties. But the situation is deteriorating rapidly:

Shrinking inventory. Every month, the global pool of S5 CPUs, I/O modules, and power supplies gets smaller. When a module fails, it gets scrapped. When a plant migrates away from S5, their spare modules get sold — but eventually these also get used up. There is no new production. The supply is finite and shrinking.

Rising prices. S5 CPU modules that cost €200–500 new in the 1990s now sell for €800–3,000+ on the refurbished market. Specialized modules (communication processors, analog I/O, positioning modules) can cost 5–10× the original price — if they can be found at all.

Uncertain quality. Refurbished modules have been in service for 20–40 years, then repaired and tested. Even with a warranty, a refurbished module has a higher failure probability than a new one. Some sellers offer "as-is" modules with no warranty at all.

No repair possible. When Siemens stopped S5 support, they also stopped accepting S5 modules for repair. Some third-party repair services exist, but they are limited to specific module types and cannot replace proprietary Siemens components.

The Knowledge Drain Is Accelerating#

The engineers who designed, programmed, and commissioned S5 systems in the 1980s and 1990s are retiring. This is not a future risk — it is happening right now:

Programming knowledge: S5 AWL (Instruction List) is fundamentally different from modern S7 SCL or IEC 61131-3 languages. Younger engineers learn TIA Portal, not STEP 5. Finding someone who can debug an S5 program is becoming as difficult as finding someone who can repair a typewriter.

System knowledge: The technician who knew that "Timer T12 controls the cooldown sequence and must be set to exactly KT 045.2 because the pump needs 45 seconds to reach pressure" — that knowledge exists only in that person's head. When they leave, it leaves with them.

Software tools: STEP 5 runs on DOS or Windows XP. The programming cables (PG cable with AS511 protocol) require legacy serial interfaces that modern laptops do not have. Even if you find someone who knows S5, they may not have the tools to connect.

The Risk Calculation Is Clear#

The cost of doing nothing is not zero. It increases every year:

Year 1 after S5 EOL (2021): Spare parts still available, prices slightly elevated. Migration cost: baseline.

Year 3 (2023): Some modules becoming scarce. Refurbished prices up 50–100%. Knowledge holders starting to retire. Migration cost: +20%.

Year 5 (2025): Critical modules hard to find. Prices 3–5× original. Key personnel gone. Programming tools on aging hardware. Migration cost: +50%.

Year 7+ (2027+): Spare parts lottery — you may not be able to find what you need at any price. No one left who understands the code. STEP 5 software no longer runs on any available hardware. Migration cost: +100% or more, because you may need to reverse-engineer the entire system from scratch.

The worst case: An S5 CPU fails on a Friday afternoon. No spare in the cabinet. The refurbished dealer can ship one in 5–7 days. Your production line is down for a week. Cost: €50,000–500,000 in lost production — far more than the entire cost of a planned migration.

The S7-300 Is Next — Don't Create a Chain Migration#

If you are considering migrating from S5 to S7-300 because it seems like a smaller step: don't. The S7-300 entered its own product discontinuation (PM410) on October 1, 2025. Standard deliveries have ended. Spare parts are guaranteed only until October 2033.

Migrating S5 → S7-300 today means migrating S7-300 → S7-1500 within 5–8 years. That is two migration projects instead of one, with double the cost and double the disruption. The only future-proof target is the S7-1500 with TIA Portal.

What a Planned Migration Looks Like#

A planned S5→S7-1500 migration is a controlled, predictable project:

1. Analysis (1–2 weeks): Document the S5 program, create I/O map, list timers and data blocks
2. Hardware selection (1 week): Choose S7-1500 CPU, I/O modules, communication setup
3. Software conversion (2–4 weeks): Convert AWL to SCL, map addresses, convert timers
4. Testing (1–2 weeks): Simulate in PLCSIM, test with real I/O
5. Cutover (1 weekend): Switch from S5 to S7 during planned downtime
6. Stabilization (1–2 weeks): Monitor, fine-tune, resolve any issues

Total timeline: 6–12 weeks. Total cost: predictable, budgetable, and manageable.

Compare this with an emergency migration after a catastrophic S5 failure: no documentation, no time to test, no option to plan, and a production line losing money every hour.

Start Today — Even If You Can't Migrate Tomorrow#

If a full migration is not in this year's budget, at least take these preparedness steps now:

1. Back up every S5 program — today, not next month
2. Document the I/O wiring while the system is running and someone still understands it
3. Stock critical S5 spare parts — CPU, power supply, and the most-used I/O modules
4. Identify the migration target — S7-1500 CPU selection and I/O concept
5. Get a migration cost estimate — so you can budget for next year

Frequently Asked Questions#

How much longer will S5 spare parts be available?

Nobody knows with certainty. Third-party dealers currently stock S5 modules, but inventory is shrinking and prices are rising every year. Common modules (standard digital I/O, power supplies) are still available. Specialized modules may already be unavailable.

Is it safe to keep running an S5 system?

The S5 hardware itself does not suddenly stop working because Siemens ended support. If the hardware is functional and you have spare parts, the system continues to run. The risk is that you cannot repair it when something fails — and failure becomes more likely as components age.

What is the minimum I should do right now?

Back up every S5 program and document the I/O wiring. These two actions take a few hours and cost nothing. They are the difference between a manageable migration and a catastrophic reverse-engineering project.

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Maintained by PLCcheck.ai. Last update: March 2026. Not affiliated with Siemens AG.