Parts, trucks, and first-time fix: plumbing inventory that stops the bleeding

Inventory feels like a back-office chore until you add up what it actually costs you: the mid-job supply-house runs, the callbacks for a fitting or cartridge you didn’t have, the fixtures that “walked off,” the money tied up in dead stock in the shop. A plumbing business with no real inventory system bleeds a meaningful chunk of its inventory value every year: carrying costs run in the 20-30% range, and write-offs, expediting fees, and stockout-driven lost jobs pile on top. This is the system that stops the bleeding, and it pays off most in the one number customers feel: first-time fix.

First-time fix is the metric that ties it all together

First-time-fix rate (FTFR), the share of calls resolved in one visit, is the operational heartbeat. Field-service benchmarks cluster around 70-80%; shops without an inventory system lag noticeably lower, the target is 80%+, and top operators push into the high 80s and low 90s. Every point of FTFR you gain is a callback you don’t eat, a customer who trusts you more, and a billable hour you keep. Most FTFR misses trace back to two things: misdiagnosis and not having the part on the truck. This guide is about the second. (For the numbers side of running the shop, see know your numbers.)

The real cost of a single stockout

Put a number on the supply-house run so the whole team takes stocking seriously. A single mid-job stockout is rarely just “a quick trip”; it stacks up:

• Windshield time to the supply house and back: real paid tech time, often the better part of an hour once you count parking, the counter line, and the drive.
• Fuel and vehicle wear on top of that.
• Supply-house counter markup over your wholesale/distributor price on the part you grabbed in a hurry.
• The lost or delayed billable call you had to push to make room for the trip, the biggest hidden cost, because it’s revenue you never invoice.

Do that a few times a week across a fleet and it adds up fast, and it’s invisible on the P&L because it’s scattered across a dozen line items. Attach one honest dollar figure to it (your own numbers) and post it where techs see it.

Stock trucks by actual usage, not a generic list

The biggest truck-stock mistake is loading every van with the same manifest. Build each van’s stock from that tech’s real last-12-months usage. A service tech doing residential repairs in older neighborhoods needs a very different kit than someone running repipes, water-heater swaps, or drain work. Start from your high-velocity failure parts, then tune per tech and per the housing/fixture mix in their territory.

A working starting point for a residential service van (trim to what your calls actually consume):

• Fittings: copper and PEX in your common sizes (1/2“, 3/4“), CPVC where you see it, plus push-fit couplings/elbows and ProPress fittings if you run the tool. No-hub couplings and dielectric unions.
• Valves: angle stops and straight stops (compression and threaded), quarter-turn ball valves, hose bibbs, and a few gate/multi-turn replacements.
• Wax rings and flanges: standard and extra-thick wax rings, waxless seals, closet flanges and repair rings, closet bolts.
• Supply lines: braided stainless faucet and toilet connectors in the common lengths; dishwasher and ice-maker lines.
• Cartridges and stems: the cartridges for the faucet brands you see most (Moen, Delta, Kohler, Price Pfister), plus common washers, O-rings, and stem kits.
• Toilet guts: fill valves, flappers, flush valves, tank-to-bowl kits, and float assemblies.
• Water-heater parts: T&P relief valves, thermocouples/thermopiles, upper and lower elements and thermostats, anode rods, and flex/dielectric connectors.
• Drain trim: P-traps, tailpieces, slip nuts and washers, pop-up assemblies, basket strainers.
• Consumables: PTFE tape, pipe dope, solder and flux, cutting wheels, sandcloth, and shark-bite disconnect clips.

Treat every van as a named inventory location. Parts loaded onto a van are a transfer; parts used on a job are a deduction tied to that work order. Without that structure, truck stock becomes a black hole: you can’t reorder accurately, you can’t see shrinkage, and you can’t trust any count.

Min/max reorder points

Stop reordering by gut. Set a reorder point per SKU from real consumption:

Reorder point = (average daily demand × supplier lead time) + safety stock

Two things make the formula actually work. First, run a 30-day parts-usage log before you set any min/max: gut-based stocking is the silent killer, and you’ll be surprised which SKUs actually move. Second, set lead-time buffers per SKU, not one generic number: an off-the-shelf wax ring restocks same-day, but a specific faucet cartridge, a water-heater part, or a backorder-prone fixture can take a week or more. Also cap each van’s stock value at a sane multiple of its monthly usage; anything beyond that is dead weight that just ties up cash and invites shrinkage. Automate reordering where your software supports it, but only once your counts are trustworthy (below).

Plumbing is less brutally seasonal than HVAC, but it isn’t flat: cold snaps drive frozen/burst-pipe and water-heater work, spring and heavy rain drive sump-pump, backflow, and drain/sewer calls, and holidays spike disposal and drain jobs. Nudge the min levels on those parts ahead of their season and review levels at least quarterly so you’re stocked before the wave, not scrambling during it.

Shrinkage and accuracy: you can’t automate what you can’t trust

Two numbers gate everything:

• Inventory accuracy needs to be high (think 95%+ on high-frequency items) before you can trust automated reordering. Manual, memory-based processes run far lower, which means a large share of parts are miscounted, mislocated, or don’t exist. Cycle-count high-velocity SKUs regularly instead of one dreaded annual count. Small shop (a truck or two)? Don’t chase 95% across everything on day one. Start by cycle-counting your top ~20 SKUs and expand from there.
• The #1 accuracy killer is the verbal “I used a couple of stops and a wax ring.” Require techs to scan or photograph every part as it comes off the truck at job close, tied to the work order. Memory-based logging is where counts (and billing) fall apart.
• Shrinkage hides in untracked truck stock, unbilled parts, and walk-off. Hold it tight (aim for the low single digits, and treat anything creeping toward double digits as a problem to hunt down). Call out warranty and “goodwill” parts as their own bucket: the flapper or supply line you throw in on a no-charge return visit is real shrinkage that otherwise disappears. Put the shrinkage dollar figure on a monthly P&L line so you feel it, not just a percentage.

Use software, and connect it to the job

Manual spreadsheets break down past a couple of trucks. Field-service and inventory platforms track parts across warehouse and vans, deduct on work-order completion, trigger reorder points, and, critically, make sure every part used gets billed to the job. Unbilled parts are pure margin leak and a shrinkage source. Connecting inventory to invoicing is where a system pays for itself twice: fewer stockouts and fewer give-away parts. If you haven’t picked a platform yet, start with choosing field-service software, and make sure the parts you promise on the phone are the ones on the truck when the tech arrives. See call handling and booking rate.

Checklist

• Measure your first-time-fix rate; target 80%+ and treat “didn’t have the part” misses as an inventory problem to fix.
• Put a dollar cost on a stockout (your own numbers) so the team takes truck stock seriously.
• Build each van’s stock from that tech’s 12-month usage, not a generic list; start from the fittings/valves/wax-rings/supply-lines/cartridges core above.
• Make every van a named inventory location; loads = transfers, uses = deductions on the work order.
• Run a 30-day usage log first, then set min/max per SKU (demand × lead time + safety stock) with per-SKU lead-time buffers; nudge seasonal parts ahead of their wave; review quarterly.
• Scan/photograph every part at job close (no verbal logging); cap each van at a sane multiple of monthly usage.
• Hold inventory accuracy high (95%+) (cycle-count high-velocity SKUs; small shops start with top ~20) before trusting auto-reorder.
• Drive shrinkage to low single digits; track warranty/goodwill giveaways separately; put the dollar figure on a monthly P&L line.
• Run it in inventory/field-service software that bills every used part to the job.

The bottom line

Inventory is a margin story disguised as a chore. Every supply-house run is lost time and a callback risk; every foot of untracked truck stock is shrinkage; every unbilled fitting is give-away profit. Stock trucks by real usage, treat each van as a tracked location, set reorder points from a real usage log, hold your counts accurate, and let software bill every part. Do it and your first-time-fix rate climbs toward 90%, which your customers feel, your techs appreciate, and your P&L quietly rewards.

General information for plumbing business owners in the US and Canada. Benchmark figures are industry ranges that vary by shop size, service mix, and region. Track your own usage and costs.