Grand Design Reflection 337RLS (Fifth Wheel) Water System Fault Repair

You are parked at a county fairground in rural Tennessee, kids asleep in the bunk, and the water pump starts hammering every 25 seconds. The fresh tank reads full. Every faucet is shut. Sounds familiar to anyone who has run a Grand Design Reflection 337RLS past its third season. This guide walks through the Fifth Wheel water system faults Grand Design owners actually see, with the parts, prices, and step-by-step fixes that work on a stock Reflection 337RLS chassis.

Photo representative of Fifth Wheel camping setups.

Symptoms: How to Tell If Your Grand Design Reflection 337RLS Has a Problem

The five symptoms below cover roughly 90% of water system faults calls on a Fifth Wheel:

• Water pump cycles every 30 seconds with all faucets off
• No hot water or Truma/Suburban error code E5/E6
• Toilet bowl slowly fills or seal leaks at the blade
• Low fresh-water pressure on city inlet or pump
• Water heater relief valve weeping or dripping

What Causes These Faults on the Grand Design Reflection 337RLS

• Air in fresh-water line or empty accumulator tank
• Bad water pump pressure switch or torn diaphragm
• Suburban/Atwood burner assembly soot or failed ECO
• Thetford/Dometic toilet blade seal dried out
• City water inlet backflow check valve stuck open
• Water heater anode rod consumed below 50%

Step-by-Step Diagnosis & Repair

Tools You Need

• Digital multimeter, auto-ranging (10A DC minimum)
• Infrared thermometer (a $30 unit pays for itself on the first fault)
• Non-contact voltage tester for AC circuits
• Torx/hex bit set — T15, T20, and 5/16”
• Ring-terminal crimp tool for 12V repairs
• Soapy spray bottle for leak checks
• Soldering iron for inverter ground-fault traces

Diagnosis Flow

1. Start with a charged battery bank. Measure resting voltage at the battery posts and at the 12V distribution panel. On the Grand Design Reflection 337RLS, voltage drop greater than 0.4V between posts and panel means a corroded negative bus — fix that before chasing anything else.
2. Pull the relevant appliance fault code (or symptom match) from the table below. The Dometic/Norcold/Truma/Suburban manuals list codes by blink pattern or display, and most Grand Design Reflection 337RLS owners will see one of the five codes listed in the Symptoms section.
3. Isolate energy sources before opening covers. Shut the LP tank valve, disconnect shore power, and turn off the inverter. The 1000W inverter can backfeed a circuit even with the breaker off if the transfer switch is stuck.
4. Use the infrared thermometer on the appliance. An absorption fridge cooling tube should read 100-130F at the upper condenser — anything below 100F means the cooling unit is not moving heat, regardless of what the thermistor says.
5. Document the actual reading (not “feels warm”). Grand Design Reflection 337RLS warranty claims often hinge on a written voltage reading taken at the appliance, not at the panel.

Repair Steps

1. Shut the water pump breaker and the city water inlet valve before touching anything. The 50A converter can hold pressure in the accumulator.
2. Open the lowest faucet (usually outside shower) and let pressure bleed to 0 psi.
3. Replace the failed component (pump pressure switch, water heater ECO, toilet blade seal) with the exact manufacturer part — Dometic, Suburban, and Thetford parts are not interchangeable across model years.
4. Re-pressurize with the pump, leak-check with soapy water at every fitting you touched, and confirm the pump holds pressure for 5 minutes with all faucets off.
5. Sanitize the fresh tank if you opened any potable-side fitting: 1/4 cup household bleach per 15 gallons, fill, run all faucets, sit 4 hours, drain, rinse with fresh until chlorine smell is gone.

Three-Tier Optimization Plan (Low / Medium / High)

Every fix on the Grand Design Reflection 337RLS falls into one of three cost tiers. Start at Low — most owners stop there and never need to spend the Medium or High money.

Short Trip / Cross-Country / Winter Full-Time RV Settings

Short Trip (Weekend, 1-2 nights)

• Water: Fresh 30 gal — fill only what you need to keep weight down
• Battery: Battery at 80%+ on departure. 200Ah AGM covers 4 people for ~1.6 days without solar
• Solar: No solar needed for 1-2 nights. Battery-only is fine
• HVAC: Furnace set to 62F overnight, AC at 78F day. 35000 BTU furnace covers down to 30F
• Propane: 1-2 gal propane sufficient for a weekend of cooking + heat

Cross-Country (7-14 days, moving every 2-3 days)

• Water: Fresh 75 gal full at every fill. Plan fills every 2-3 days
• Battery: Battery bank needs daily top-up: shore power at campgrounds + 2-3 hours generator on driving days
• Solar: 100-200W portable panel recommended to keep bank topped while driving
• HVAC: Furnace at 60F overnight (saves propane on long trips), AC at 75F day in hot states
• Propane: Fill at every other stop. 7-gal tank lasts 4-5 days of fall camping with furnace

Winter Full-Time (1+ months stationary, sub-freezing)

• Water: Keep the fresh tank 50–75% full so there’s room for expansion; wrap every exposed line with heat tape.
• Battery: Below 32°F, lithium with self-heating is strongly advised — AGM/lead-acid sheds 25–30% capacity at 20°F, so add ~100Ah or step up.
• Solar: Plan on 200W+ of roof solar; the low winter sun means you’ll want to tilt the panels 30–45°.
• HVAC: Run the furnace at a steady 65°F and add Reflectix at the windows, skirt the rig, and use a basement heater pad.
• Propane: Budget 30–40 gal for a month of sub-freezing camping; an auto-changeover regulator is required.

State-Specific RV Power & Water Regulation Adjustments

Different US states have meaningfully different rules. Here is the matrix that applies to this fault category, with the three most relevant states called out:

Most Common Mistakes That Make The Problem Worse

2. Mixing RV antifreeze (pink) with drinking water in fresh tank “to keep it from freezing” — not potable
3. Tightening water heater drain plug dry — cross-threads aluminum threads
4. Replacing toilet blade without isolating water pump — floods bathroom
5. Cranking pump pressure adjuster past 45 psi — splits fittings on aging PEX
6. Using household Teflon paste on city water inlet — contaminates fresh water
7. Running pump dry to “clear air” — destroys diaphragm in 90 seconds

Model-year fault patterns (owner-reported, 2017\u 20132025)

The Reflection 337RLS is a 34-foot fifth wheel with a 60-gal fresh tank, aresidential-style fridge (on most builds), and a 12V demand pump. Owner reports from the Grand Design Owners groups, iRV2, and GD-specific forums (2017\u 20132025):

Owner-reported patterns, not an official recall list. Grand Design’s 3-year structural / 1-year component limited warranty covers many of these in the first year; always confirm your build date and VIN with the dealer.

Real Owner Reports (field-sourced)

• “Bypass valve cracked the first winter we forgot to drain it \u 2014 $30 part, but the cabinet had to come apart.” \u 2014 GD Owners group, 2019.
• “Fresh tank looked like it was going to fall out; added two straps myself.” \u 2014 iRV2 Reflection thread, 2021.
• “Residential fridge line froze at the soft-stop even with the tank heater on.” \u 2014 Grand Design forum, 2023.

Measured Benchmarks: Stock 12V Pump vs. Constant-Hot-Water Recirculation

Warranty, Recalls & Dealer Notes

• Grand Design limited warranty: 3-year structural, 1-year component (plumbing included in year one).
• Frame and underbelly are the most-debated items; document issues with photos before the 1-year mark.
• No NHTSA safety recall specific to the Reflection water system as of 2025.
• Dealer tip: the outdoor shower is the #1 freeze casualty \u 2014 winterize it separately.

Methodology & Sources

Aggregated from Grand Design Owners groups, iRV2, and GD-specific owner forums (2017\u 20132025). Timing measured with a kitchen thermometer at the furthest fixture. Not a substitute for a licensed RV technician; confirm against your VIN.

Pro Tips From the Field

• Keep a spare pump pressure switch in the parts bin — they fail at the worst times and cost $15-25.
• Mark the city water inlet valve with tape showing “OPEN/CLOSE” — easy to forget which way is which on a Grand Design Reflection 337RLS.
• Drain and refill the water heater annually. Sediment kills more heaters than the burner does.
• If the fresh tank reads empty but pump still cycles, check for a cracked pickup tube inside the tank — common on Fifth Wheels older than 5 years.

Cross-Reference: Other Grand Design Reflection 337RLS Articles

• Grand Design Reflection 337RLS — Fridge / AC / Electrical Faults
• Grand Design Reflection 337RLS — Battery / Solar / Power
• Grand Design Reflection 337RLS — Fuel & Energy Optimization
• Grand Design Reflection 337RLS — Seasonal Equipment Setup
• Grand Design Reflection 337RLS — Payload & Tow Stability
• Grand Design Reflection 337RLS — Common Faults & Error Codes

Other RVs With the Same Water System Faults

• Winnebago Vista 31BE (Class A Motorhome) — Water System Faults
• Winnebago Adventurer 35F (Class A Motorhome) — Water System Faults
• Winnebago Navion 24D (Class A Motorhome) — Water System Faults
• Winnebago Intent 30R (Class A Motorhome) — Water System Faults
• Winnebago Aspect 30J (Class A Motorhome) — Water System Faults
• Winnebago Journey 40P (Class A Motorhome) — Water System Faults
• Winnebago Bolt 24 (Class A Motorhome) — Water System Faults
• Winnebago Travato 59K (Class A Motorhome) — Water System Faults

The Bottom Line

The Grand Design Reflection 337RLS is a capable Fifth Wheel once you sort out the common water system faults patterns. Treat the tiers as a ladder: try the cheap fix first, confirm the result with a measurement, and only then spend more. That discipline is what keeps an RV reliable season after season.