Hydrovac Troubleshooting Guide: Common Problems and How to Fix Them

I've been wrenching on hydrovac trucks for over 25 years now, and I can tell you this: most breakdowns happen because someone ignored the early warning signs. The good news? Most problems follow predictable patterns. If you know what to look for, you can often fix it yourself or at least know exactly what's wrong before you call for help.

This is my complete troubleshooting guide covering the problems I see most often. I'm going to give it to you straight — what's actually wrong, what you can fix yourself, and when you need to call in a pro.

The Big Five: Most Common Hydrovac Problems

In my experience, about 90% of the calls I get fall into these five categories:

1. Vacuum won't build — Usually a stuck relief valve or bad door seals. This is the most common call I get, and it's often fixable in the field.

2. Boom won't rotate or extend — Hydraulic issues, usually a bad motor, stuck valve, or low fluid. Can strand you mid-job if you're not careful.

3. Water pressure dropping — Could be the pump, could be as simple as a clogged filter. I've seen guys replace pumps when all they needed was a $20 strainer.

4. PTO won't engage — Electrical, mechanical, or just an adjustment issue. This one makes guys panic, but it's usually straightforward.

5. Debris tank won't dump — Hydraulic lift problems, valve issues, or mechanical binding. Heavy tank full of mud and nowhere to put it — that's a bad day.

Each of these has its own detailed guide linked above. But let me give you the quick rundown on diagnosing each one.

Quick Diagnosis: Where to Start

When something goes wrong, your first job is figuring out which system is actually failing. Here's my quick checklist:

If nothing works at all:

• Check your PTO engagement first
• Look for blown fuses or tripped breakers
• Verify engine RPM is high enough for PTO operation
• Check for error codes on newer trucks

If vacuum-related systems fail:

• Relief valve stuck open (most common)
• Door seals leaking
• Blower issues (worn lobes, bad bearings)

If hydraulic systems fail (boom, tank lift, outriggers):

• Check fluid level first — always
• Look for obvious leaks
• Check if the pump is running (you should hear it)
• Feel the hydraulic lines — cold means no flow

If water system fails:

• Check the obvious: is there water in the tank?
• Look at your strainer/filter
• Check pump prime
• Feel if pump housing is hot (overheating = problem)

The "Is It Even Running?" Test

I can't tell you how many times I've driven out to a job site just to find something wasn't actually turned on or engaged. Before you tear anything apart, verify the basics:

1. PTO engaged? That dash light isn't always reliable. Get out and look/listen.
2. Engine RPM up? Most systems need 1200-1500 RPM minimum to function.
3. Emergency stops reset? Check every E-stop on the truck.
4. Circuit breakers in? There are usually several — check them all.

I had a call last month from a contractor in New Jersey who was convinced his entire hydraulic system was shot. Drove out there to find the E-stop behind the operator panel was bumped during loading. Thirty seconds to diagnose, zero parts needed. He felt stupid, but honestly, it happens more than you'd think.

Understanding Your Hydrovac Systems

Your hydrovac has several interconnected systems, and understanding how they work together helps with troubleshooting:

The Vacuum System Your PD blower creates vacuum in the debris tank. Air (and material) gets sucked in through the boom. The relief valve prevents over-vacuum. The debris tank door seals keep the vacuum contained. If any of these fail, vacuum drops.

The Hydraulic System One pump typically powers multiple functions: boom rotation, boom extension, debris tank lift, and sometimes outriggers. The pump draws from a reservoir, pushes through control valves, and actuates cylinders or motors. Low fluid affects everything. A stuck valve affects only that function.

The Water System Water tank → pump → heater (if equipped) → hose reel → nozzle. Simple in concept, but the pump is the heart. Water pump failures are common because these pumps work hard — 2000+ PSI in some cases.

The Diesel Engine This powers everything through the PTO. Engine problems can masquerade as other issues. If your engine's struggling, everything else suffers.

Seasonal Problems to Watch For

Different seasons bring different headaches:

Winter Issues:

• Frozen relief valves (extremely common)
• Water system freeze damage
• Thickened hydraulic fluid
• Diesel gelling
• Weak batteries

I wrote a whole guide on winter hydrovac preparation — worth reading before the first freeze hits.

Summer Issues:

• Overheating (engine, hydraulic, water pump)
• Dust contamination in filters
• Hydraulic system running hot
• A/C failures (okay, that's comfort, but still)

Year-Round:

• Worn door seals (vibration and use)
• Hydraulic leaks (constant pressure cycles)
• Electrical gremlins (vibration, moisture)

When to Fix It Yourself vs. Call for Help

Here's my honest take on what you can handle versus what needs a pro:

Fix It Yourself:

• Stuck relief valve — tap it free, spray some lubricant
• Low hydraulic fluid — top it off
• Clogged water strainer — clean or replace it
• Blown fuse — replace it
• PTO adjustment — if you know what you're doing
• Door seal — temporary fixes in the field, permanent fix later

Call for Help:

• Blower making grinding noises — shut it down, call immediately
• Hydraulic pump whining/screaming — internal damage happening
• Electrical problems you can't trace — don't chase your tail
• Anything involving opening up major components
• Any problem you've tried to fix twice and can't

The key is knowing your limits. I've seen guys turn a $500 repair into a $5,000 repair by taking things apart they shouldn't have. There's no shame in calling for help.

Preventive Maintenance: Stop Problems Before They Start

Most of the emergency calls I get are from trucks that haven't been properly maintained. Here's what actually prevents breakdowns:

Daily:

• Check hydraulic fluid level
• Look for obvious leaks
• Test door seal (dollar bill test)
• Listen for unusual sounds during startup

Weekly:

• Check blower oil level
• Inspect water strainer
• Grease boom pivot points
• Check belt tension and condition

Monthly:

• Change blower oil (or every 200 hours)
• Inspect all hydraulic hoses
• Check electrical connections
• Test all safety systems

Seasonally:

• Full maintenance inspection
• Hydraulic fluid analysis
• Winterization before cold weather
• Complete system testing

For fleet operators, I offer fleet maintenance programs that handle all of this on a schedule. Cheaper than emergency repairs, every time.

My Tool Recommendations for Field Repairs

Keep these in your truck and you can handle most minor issues:

• Basic socket and wrench set
• Multimeter (for electrical diagnosis)
• Hydraulic pressure gauge (worth the investment)
• WD-40 or penetrating oil
• Extra hydraulic fluid (1-2 gallons)
• Spare fuses and relays
• Zip ties and electrical tape
• Flashlight (sounds obvious, but...)
• The number of a good mobile mechanic

Getting Help Fast

When you do need help, here's how to get it faster:

1. Know your truck: Year, make, model, and what brand of hydrovac body (Vactor, Guzzler, Vac-Con, etc.)
2. Describe the symptom clearly: "Boom won't rotate left but rotates right fine" is better than "boom's broken"
3. Tell me what you already tried: Saves me from suggesting things you've done
4. Know your location: GPS coordinates help if you're on a job site in the middle of nowhere

I provide mobile hydrovac repair throughout Pennsylvania, New Jersey, New York, and the DC/Maryland area. Most of the time I can get to you same day if you call early enough.

The Bottom Line

Hydrovac trucks are complicated machines, but they fail in predictable ways. Learn the common failure points, do your preventive maintenance, and know when to call for help. That's how you keep these trucks running and money coming in.

Check out the detailed troubleshooting guides I linked at the top of this article for specific problems. And if you're stuck right now, call me at 272-296-9637. I've probably seen your exact problem a hundred times.