---
title: "Aging Control Systems: How to Know When It's Time to Upgrade"
description: Jacob Foglia, Lead Automation Engineer, shares the signs of an aging control system, the hidden costs of waiting, and how to plan an upgrade on your terms.
---

[Premier Automation Blog](https://info.premierautomation.com/blog)

# [Aging Control Systems: How to Know When It's Time to Upgrade](https://info.premierautomation.com/blog/aging-control-systems-how-to-know-when-its-time-to-upgrade)

 Written by [Cecelia Rice](https://info.premierautomation.com/blog/author/cecelia-rice) | Oct 22, 2026, 5:40:26 PM

When Siemens or Rockwell announces that a product is being phased out, plants typically have about ten years of manufacturer support before that product becomes difficult to replace. That is a long runway, with enough time to budget, plan, and migrate on your own schedule. Yet Jacob Foglia, Lead Automation Engineer at Premier Automation, regularly works in plants where the core control system went obsolete a decade or more before anyone started planning its replacement.

The delay is rarely careless. Control systems that have run reliably for years tend to stay low on the priority list, and when production is steady, there is little pressure to spend capital on equipment that still does its job. The upgrade decision gets made either way, though. Plants that use the phase-out window make it on their own terms, with a budget and a schedule in place. Plants that let the window pass usually have the decision made for them by a failure, with far fewer options for getting back online.

Drawing on Foglia's experience with legacy systems, this guide covers the signs a control system is aging, why deferring an upgrade feels reasonable and where that reasoning breaks down, and how to make the decision while you still control the timing.

## What Are the Signs Your Control System Is Aging?

Aging control systems tend to show the same handful of warning signs: replacement parts that are harder to source, trouble interfacing to newer equipment, alarms that no longer reflect what is happening on the line, missing documentation, and engineering software that only runs on unsupported versions of Windows.

### Replacement Parts Are Harder to Find

The most common sign is difficulty sourcing parts. When manufacturers like Siemens or Rockwell stop listing a component, replacements shift to third-party resellers and online marketplaces, where pricing, condition, and availability are hard to predict.

### New Equipment Can't Communicate With the Existing System

Most integration projects add new equipment to an existing line rather than building a plant from scratch. If the controls around a new machine are too old to communicate with it, you may need specialty gateway hardware just to get the two to interface. Older serial networks such as DeviceNet, Data Highway, and Profibus are common sources of this problem as plants move toward Ethernet-based protocols.

### Alarms No Longer Reflect What Is Happening on the Line

Over time, operators can grow used to alarms that never clear. Foglia regularly sees HMIs showing dozens of active alarms on lines that are running normally, usually because sensors were disconnected or broken and the logic was adjusted to work around them. When a real fault occurs, it is easy to miss among alarms everyone has learned to dismiss.

### Electrical Prints and Program Backups Are Missing

Missing electrical prints and program backups are among the most commonly overlooked warning signs, and Foglia notes they often turn up where you would least expect them.

> *“Sometimes it's the reliable equipment, the machines that have run well for 10 or 15 years. The engineer who oversaw the machine installation left or retired, and the prints and code backups seemingly went with them.”*

When a system rarely needs troubleshooting, nobody notices the documentation is gone until the day it is needed. If a PLC battery fails and the program is lost, or a forklift damages a conduit run, your team has nothing to restore or rebuild from.

### Engineering Software Won't Run on a Supported Version of Windows

Foglia regularly sees engineering software for PLCs and HMIs that is only compatible with Windows 7 or Windows 10. Both operating systems are now past the end of Microsoft support, with Windows 7 support ending in 2020 and Windows 10 support ending in 2025. Without regular Windows updates, the computers your team uses to program and troubleshoot the control system no longer receive security patches, which adds risk every time they connect to your equipment. When the software you need to maintain a system can't run on a supported operating system, it is a strong sign the platform behind it is due for an upgrade.

### Maintenance Issue or Upgrade?

Not every failure means the system needs replacing. A dead power supply, a failed relay, a burned-out cabinet fan, or a clogged filter are maintenance issues, often involving parts under $100. The conversation shifts to replacement when the manufacturer announces a phase-out of your core platform, particularly the PLC.

## Why Do Plants Wait, and What Does It Cost?

Manufacturers publish a lifecycle status for every product. A part starts as active, available at normal pricing and lead times. Once the manufacturer announces a phase-out, the part enters a support period where it is still available but no longer recommended for new installations. After cancellation, new units are no longer sold, and you are left with refurbished stock, repairs, or the secondary market. Knowing where your equipment sits in that cycle tells you how much runway you have left, but it does not explain why so many plants let the runway run out.

### Why Deferring an Upgrade Feels Reasonable

From a budget perspective, waiting often looks like the smarter choice. Foglia is candid about the math plant managers face.

> *“It's easier to pay a thousand bucks on eBay every couple of months than spend 200,000.”*

A full migration can mean a six-figure investment and a week or more of downtime, while keeping the old system alive costs a few replacement parts a year. How plants purchase parts reinforces that choice. Many facilities Foglia works with have a monthly electrical maintenance purchasing limit, often somewhere between $10,000 and $50,000. A replacement part from a reseller, even at a steep markup, usually falls under that limit and can be bought without capital approval. A full upgrade becomes a capital expenditure, which brings more review, more approvals, and a longer timeline. As a result, the purchasing process itself steers teams toward keeping the old system running.

The problem is that the risk does not grow at the same steady pace as those small expenses. Each year the system runs, the supply of replacement parts shrinks and the people who know the platform retire or move on. The system can look stable for years, right up until a CPU or I/O card fails and there is no replacement on the shelf. At that point, the plant is no longer weighing a planned project against a small recurring cost. It is facing an unplanned outage with no clear end date, followed by the same migration it had been deferring.

### The Hidden Costs of Running Past End of Life

The costs of an aging system build gradually, starting with parts. Manufacturers often raise prices on phased-out components to encourage migration, and third-party pricing climbs as supply shrinks. When a part cannot be found quickly, plants sometimes resort to cannibalization, pulling components from one line to restart another.

Expertise becomes harder to find as well. As engineers with hands-on experience on older platforms retire, fewer people can troubleshoot those systems quickly, and much of the knowledge that remains lives with one or two people inside the plant. Internally, your engineering team spends more of its time keeping an old system running and less on projects that improve the operation.

Waiting can also make the eventual project more expensive. One customer recently told Foglia he adds five to ten percent to every budgetary quote, expecting pricing to change by the time the project is approved.

### Modernization Opens Up Data, and New Responsibilities

One cost of an aging system is easy to miss because it shows up as a missed opportunity. Older platforms make it difficult to pull the machine data that drives analytics and predictive maintenance, which limits your visibility into how the equipment is performing and when it is likely to fail. Access to that data is one of the strongest arguments for modernizing.

Foglia points out that connectivity comes with a tradeoff. An older, air-gapped system with no connection to the internet has no path for a remote attack. Once a system is connected to a plant network or the cloud to share data, it needs to stay current, because Siemens and Rockwell regularly release firmware updates to close newly discovered security vulnerabilities. Before you upgrade, decide how connected the new system needs to be, and plan for ongoing patching and coordination with your IT team as part of the investment.

## How Do You Decide When to Upgrade?

The decision starts with knowing where your system stands and reducing the risk you can control today. From there, it depends on what your organization can support and how well engineering, production, and leadership agree on timing.

### Reduce Your Risk Before You Spend Capital

The best first step is to check your PLC and programming software. The PLC is the brain of the system, so if it is obsolete, the equipment it communicates with likely is as well. Search each part number along with “product lifecycle” on the manufacturer's website to see its current status, and check whether your system relies on one of the legacy communication networks mentioned above.

While you plan, there are several low-cost steps that lower your exposure right away. Back up every PLC and HMI program and store copies somewhere other than the machine itself. Update or recreate electrical prints for critical lines. Keep a spare CPU and spares for your most critical I/O cards on hand, since those are the failures most likely to cause an extended outage. None of these steps requires a capital project, and each one shortens your recovery if a failure comes before the upgrade does.

### Answer Three Questions Internally

Before you call an integrator, it helps to answer three questions. First, is the budget available? Second, can you commit to downtime windows and protect them once the work begins? Third, who will support the new system once the integrator leaves? If you do not have in-house controls expertise, plan for it as part of the project.

### Align Engineering, Production, and Leadership

In almost every plant Foglia works in, there is a familiar tension between engineering and production. Engineering asks for a couple more hours to fix a problem properly instead of patching it, and production needs the line running to meet its numbers. Both are doing their jobs, and that tension is a major reason upgrades stall. It also explains why planned outages get cut short.

The way through is a shared language, and for most plants that language is downtime cost. A statement like “Our PLC is old” is easy to set aside. A statement like “Our controller is end of life, we have no spare CPU, and a failure could leave us down for at least three days while we search for a replacement” gives leadership a clear picture of the exposure, especially when paired with your plant's hourly downtime cost. Framed this way, the upgrade becomes a decision about protecting production rather than competing with it.

## Can You Upgrade Without Shutting Down Production?

Many plants hold off on upgrades because they assume a migration means taking the line down for weeks. For most operations, a full shutdown is not realistic, and on the automation side, it is often not necessary. Critical mechanical repairs may still require a full outage, but much of the controls work can be staged around them. A phased migration starts with an engineering study that breaks a one or two week commissioning effort into single-day segments. Those segments are scheduled during the maintenance windows your lines already take, replacing I/O racks and components a piece at a time until the system is positioned for a final cutover. Because each step fits within downtime production already expects, phasing also takes much of the friction out of the engineering and production conflict. Premier is using this approach now with a customer in the Southeast, working through the migration one planned outage at a time.

Premier's Automation team works across multiple PLC platforms and generations of control technology, including the legacy systems many organizations find hardest to support. Whether your system recently entered its phase-out period or passed it years ago, contact Premier to schedule an assessment and build a modernization plan that fits your budget, your downtime windows, and your production goals.

[View full post](https://info.premierautomation.com/blog/aging-control-systems-how-to-know-when-its-time-to-upgrade)

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