You Installed It But Someone Else Has Modified It: Decision Tree

Why this matters

You get called back to a system you put in, and the moment you open it up you can see other hands have been in it. This is a common, awkward spot: it is your name on the original job, but the thing in front of you is not the thing you left. Handle it wrong and you either eat a fault you did not cause or stamp your warranty on a modification you never made. This tree keeps you from both.

Start here: is anything unsafe right now

Before any diagnosis, scan for a hazard the modification may have introduced. A later change that defeats a safety function is the most dangerous thing you can find on an old install.

• Gas, combustion, or a burning smell: get people out, do not operate switches, shut off the fuel on your way out only if the shutoff is in your path, and call the utility. Diagnose nothing until it is cleared.
• Water plus electricity, a missing bond or ground, an energized surface: de-energize at the source and verify dead before you touch it.
• A defeated safety device (a jumpered pressure relief, a bypassed limit or float switch, a removed overload, a blocked flue): stop. Make it safe or shut the system down before continuing.

If it is unsafe, the safety action comes first and the responsibility conversation comes second.

Step 1: confirm it is actually your original install

Do not assume. Pull your records if you have them (invoice, photos, as-built, serials). Match what you documented against what is on the wall. If the core equipment, location, and layout match your job, proceed as your install. If they do not, you may be looking at a full replacement someone else did on the same spot. See related: Your Records Don't Match What You See On Site.

Step 2: separate your work from the later changes

Walk the system and sort every component into three piles: clearly mine, clearly added or altered later, and unclear. The tells are physical: mismatched materials, different fittings or connectors, a different workmanship signature, fresh cuts in aged material.

• If the modified area is where the fault lives, the later change is your leading suspect. Go to Step 3.
• If the fault is in an untouched part of your original work, treat it as a normal aged-system diagnosis and own what is yours.
• If you cannot tell where the fault is yet, finish the diagnosis before assigning anything.

See related: Separating Your Original Work From Later Changes.

Step 3: prove the modification caused the fault, do not assume it

A change being present near a fault does not prove it caused the fault. Isolate it: does the fault track with the modified component, does removing or bypassing the change restore normal operation, does the modification violate a rating or a code that explains the symptom. See related: A Later Modification Caused the Fault On Your Install.

If the modification is the cause, you have a clean finding: the failure started with a change you did not make.

If your original work is the cause, say so and stand behind it. Your credibility on the first case depends on your honesty on this one.

Step 4: decide how you will handle it

Now you make three separate calls, and it helps to keep them separate:

• Cause: what actually failed and why (a diagnostic finding).
• Responsibility: whose change or whose original work led to it (an attribution). See related: Who's Responsible When Your Work Was Altered.
• Whether you stand behind it: warranty, goodwill, or a paid repair, given the tampering. See related: Stand Behind Old Work That Was Tampered With, Or Not.

Recap

1. Make any hazard safe before diagnosing; a defeated safety device leads.
2. Confirm the equipment on site is actually your original install.
3. Sort every component into mine, later-changed, or unclear.
4. Prove, do not assume, that a modification caused the fault.
5. Handle cause, responsibility, and warranty as three separate decisions.

References

• Trade-standard practice for field diagnosis and lockout/tagout of unsafe equipment
• OSHA guidance on de-energizing and verifying dead before service
• See related: Separating Your Original Work From Later Changes; A Later Modification Caused the Fault On Your Install; Stand Behind Old Work That Was Tampered With, Or Not