PLC Retrofit Costs 2026: What Control System Modernization Really Costs

1.The Retrofit Urgency in 2026

"We don't have spare parts for your S7-300 anymore." More and more production managers in the Greater Region are hearing this sentence – and it marks the beginning of a ticking clock.

As an automation engineer based in Luxembourg, I experience this situation weekly: production systems that have been running reliably for 20 years are suddenly facing the end. Not because the mechanics are worn out, but because the control system has become obsolete.

The facts are clear:

• Siemens S7-300 discontinuation: Final as of October 2025 (P.M410)
• Spare parts availability: Only until approximately 2035 through primary market
• Legacy installation base: 60-70% of all SME systems in the Greater Region still run on S5/S7-300
• 85% of SMEs operate without advanced Industry 4.0 technology

2.What Does a PLC Retrofit Really Cost?

The most common question from my clients is: "What will this cost?" The answer depends on the scope – but compared to a new system, retrofit is almost always more economical.

2.1.Cost Table by Retrofit Scope

Retrofit Scope	Typical Costs	Downtime
Edge gateway overlay (data acquisition without PLC modification)	€1,000–10,000	Hours
HMI modernization (interface only)	€5,000–20,000	1–3 days
Drive modernization (frequency converters)	€10,000–40,000	3–5 days
PLC replacement (controller swap)	€30,000–150,000+	1–4 weeks
Complete retrofit with safety technology	€50,000–200,000+	2–6 weeks

2.2.The 60% Rule According to Siemens

Industry rule of thumb: Retrofit is economically sensible when costs are below 60% of new machine price. In practice, this means:

• Retrofit costs: 30-60% of a new system
• Payback period: 12-36 months
• ROI advantage: 18-24 months vs. 4-6 years for new investment

2.3.ROI Calculation: Why Retrofit Pays Off

With average downtime costs in manufacturing:

• General manufacturing: €260,000/hour (Aberdeen Research)
• Automotive: €2.1 million/hour (Siemens True Cost of Downtime 2024)
• Oil & Gas: ~€500,000/hour

Example calculation: An €80,000 retrofit pays for itself through just 20 minutes of avoided unplanned downtime in automotive manufacturing – or through 18 hours in general manufacturing.

3.Retrofit Projects in the Greater Region

Success stories from our region show what's possible – and that investments deliver measurable results.

3.1.Luxembourg: Lighthouse Projects

Husky Technologies Dudelange – FEDIL Innovation Award 2024

• Project: NGOM (Next Generation Operating Model) full digitalization
• Investment: €3.2 million in government funding
• Results: Lead time from 4-5 weeks to under 1 week, steel-to-mold in 17 minutes
• Technology: Siemens MindSphere, AGVs with 5-ton payload, digital twins

Goodyear Dudelange – Mercury Ultra-Automation

• Project: Fully automated tire manufacturing with additive manufacturing
• Investment: €64 million
• Capacity: 500,000 tires/year, 4× faster than standard process

Guardian Glass Bascharage – Furnace Modernization

• Project: Float glass line modernization
• Funding: Government investment aid
• Result: Improved energy efficiency, extended equipment lifetime

Saarland: Automotive Transformation

ZF Friedrichshafen Saarbrücken

• Project: E-mobility transformation of 9,000-employee plant
• Investment: Triple-digit million Euro amount
• Scope: Complete conversion to EV powertrain production

ZeMA Saarbrücken – SME Digital Center

• Offering: Retrofit demonstrators, 4,000 m² test field
• Partners: Airbus, BMW, Bosch, Daimler, Festo, Ford, Miele, Porsche, VW, ZF
• For SMEs: Free test environments for retrofit evaluation

Learn more about Automation Trends 2025 in Luxembourg.

4.The Migration Path: S5/S7-300 → S7-1500

For best practices in PLC programming after migration, see our PLC Programming Guide.

The technical migration is fully documented by Siemens. The key SIOS articles for your preparation:

SIOS Article ID	Topic
105106251	Complete S5→S7-1500 migration guide
109478811	S7-300/400→S7-1500 migration (hardware and software)
62100731	TIA Portal migration prerequisites
1118413	S5/S7 Converter manual
109744280	IE/PB Link PN IO (PROFIBUS-PROFINET coexistence)

4.1.Migration Path Overview

SIMATIC S5 → S5/S7 Converter (STEP 7) → STEP 7 V5.x → TIA Portal Migration → S7-1500

4.2.What Gets Automatically Converted

• Symbol tables → PLC tags
• AWL programs → Structured Text (partially)
• Standard function blocks
• Basic communication parameters

4.3.What Requires Manual Rework

• TB/TBN/SU/RU commands (bit test operations)
• System data blocks (DB0, DB1, DX0)
• Indirect addressing
• Communication blocks (PUT/GET, BSEND/BRCV)
• Failsafe functions (complete reconfiguration in TIA Portal Safety)

4.4.Hardware Compatibility Options

Siemens offers adapters for gradual migration:

• I/O adapters: Reuse existing S5 front connectors with S7 modules
• IM 463-2 Interface: Continue operating S5 expansion racks with S7 backplanes
• IE/PB Link PN IO: PROFIBUS-PROFINET coexistence for mixed networks
• ET 200 continuity: S5 ET 200 distributed I/O can continue operating with S7 systems

5.CE Marking After Retrofit

The EU Machinery Regulation 2023/1230 replaces the previous Machinery Directive 2006/42/EC as of January 20, 2027. For retrofit projects, the key question is: When does a substantial modification get triggered?

5.1.Substantial Modification Exists When ALL Criteria Are Met:

1. Modification occurs after placing on the market
2. Modification was not foreseen by the manufacturer
3. Modification affects safety (new hazard or increased risk)
4. New protective devices or stability measures required

5.2.Consequences of Substantial Modification (Art. 18, EU MR 2023/1230)

• The modifier becomes the manufacturer
• New conformity assessment required
• New technical documentation
• New EU declaration of conformity
• Affix CE marking
• Keep documentation for 10 years

5.3.No New CE Required For:

• Like-for-like component replacement (identical)
• Routine maintenance and repair
• Manufacturer-intended software updates
• Productivity optimizations without safety impact

6.7 Decision Criteria: Retrofit vs. New Equipment

The decision between retrofit and new investment depends on several factors. This checklist helps with evaluation:

6.1.1. Mechanical Condition

• Machine bed, guides, spindles still functional?
• Wear parts within acceptable range?

6.2.2. Spare Parts Availability

• Control components still available?
• Secondary market prices economically viable?

6.3.3. Production Requirements

• Existing cycle times sufficient?
• Quality requirements achievable?

6.4.4. Digitalization Needs

• MES/ERP connectivity required?
• Predictive maintenance desired?

6.5.5. Energy Efficiency

• IE4/IE5 motors economically sensible?
• Variable frequency drive deployment possible? (20-50% energy savings)

6.6.6. Safety Compliance

• CE retrofitting per EN ISO 13849 necessary?
• Performance Level (PL) requirements defined?

6.7.7. Workforce Availability

• Legacy specialists available internally?
• Training effort for new technology acceptable?

Rule of thumb: If 5 or more criteria favor retrofit and costs are below 60% of new price – modernize instead of replace.

7.Minimizing Downtime

The biggest cost factor in retrofit projects is often not the hardware, but the production loss. With proper planning, downtime can be reduced to 20-50%.

7.1.Best Practices According to Siemens and Fraunhofer

Phase 1: Preparation (no downtime)

• Complete programming and simulation in S7-PLCSIM
• Hardware pre-assembly on mounting plate
• Prepare I/O adapters for quick connection
• Document fall-back strategy (keep S5 return possible)

Phase 2: Installation (minimal downtime)

• Plan weekend/holiday installation
• Initially keep old control system in parallel
• Phase-wise switching of individual plant sections
• 24/7 integrator availability

Phase 3: Commissioning (monitored operation)

• Intensive on-site initial monitoring
• Immediate problem resolution
• Documentation of all adjustments

7.2.Typical Downtime Reduction

Project Type	Total Duration	Machine Downtime
Simple PLC migration	3-4 weeks	2-5 days
Standard CNC retrofit	12-14 weeks	4-6 weeks
Edge gateway (data acquisition only)	1-2 days	Hours (during running production)

8.Conclusion: Act Now – Two Deadlines Approaching

The facts speak clearly:

• 2035 deadline: End of S7-300 spare parts supply
• 2027 deadline: EU Machinery Regulation with new CE requirements
• Now: Optimal window for planned modernization instead of emergency retrofit

8.1.Your Next Steps

1. Inventory: Which controllers run on S5/S7-300?
2. Prioritization: Which systems are production-critical?
3. Budget: Weigh retrofit costs against downtime risk
4. Timeline: Plan migration before 2035

As an automation engineer in the Greater Region, I support you in planning and implementing your retrofit projects – from initial analysis to commissioning.

9.Further Resources

• Siemens Industry Online Support (SIOS): support.industry.siemens.com
• ZeMA Saarbrücken – Retrofit Test Field: www.zema.de
• L-DIH – Digital Maturity Assessment: www.dih.lu
• EUR-Lex – EU Machinery Regulation 2023/1230: eur-lex.europa.eu
• Fraunhofer IOSB-INA – Digitalization Toolkit: www.iosb-ina.fraunhofer.de

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About the Author: David Prybisch is an automation engineer in Luxembourg specializing in PLC modernization, retrofit projects, and worldwide commissioning. He supports companies in the Saar-Lor-Lux Greater Region with migrating legacy controls to modern S7-1500 systems.