RV Repair FAQ: 25 Questions We Answer Every Week

These are the questions our support inbox sees most, answered the way we answer them on the phone. Each answer links to the part or the longer guide.

Water and plumbing

1. Why does my RV water pump keep cycling on and off when no tap is open? A pump that cycles with everything closed is losing pressure somewhere: a dripping faucet, a leaking toilet valve, a weeping fitting, or a failed check valve inside the pump letting water flow back to the tank. Find the leak with a dry paper towel at every joint. If nothing is wet, the pump's internal check valve is the usual culprit and the fix is a new 12 V water pump. Full procedure: water pump cycling troubleshooting.

2. My water pump runs but no water comes out. What now? Check the tank actually has water, the tank valve is open, and the pump strainer is not clogged. Then check for an air leak on the suction side; a loose fitting between tank and pump lets the pump suck air instead of priming. If it hums but does not pump, the diaphragm has failed. See how to replace an RV water pump.

3. Why will my tankless water heater not light? Most no-ignition faults are low flow or low 12 V. Tankless heaters need a minimum flow rate to trigger the burner, so a clogged water filter or a water-saving shower head can stop ignition. Also confirm propane pressure and that the unit's 12 V supply is above about 11 V under load. Details: tankless water heater troubleshooting.

4. How do I winterize an RV water system? Drain the fresh tank and water heater, bypass the heater with a bypass valve, blow out the lines with a blowout adapter at low pressure, then pump RV antifreeze through every tap. Or book the Winterization Service ($183.20). Checklist: winterizing an off-road camper.

5. Why does my gray tank smell inside the camper? A dry P-trap or a failed trap seal lets tank gas back up through the sink. A HepvO waterless trap ($34.99) replaces the P-trap with a membrane valve that cannot dry out on the road. Guide: HepvO install.

6. What size fresh water tank does my Black Series HQ use? It varies by model and year. The water tank replacement guide lists fitment; OEM tanks are in the Water collection. Measure the old tank before ordering.

Batteries and power

7. How do I know if my RV battery is actually charged? Voltage is only reliable after the battery has rested for hours with no load, and it barely moves on lithium. Fit a shunt-based monitor such as the Victron SmartShunt and read state of charge as a percentage. Guide: SmartShunt install.

8. Can I charge a lithium battery from my truck's alternator? Not directly. Lithium will pull as much current as the alternator can make and can overheat it, and the alternator's voltage is wrong for lithium. Use a DC-DC charger such as the Victron Orion XS between the two. Guide: Orion DC-DC charging.

9. Lithium or AGM for an RV? Lithium if you boondock, run an inverter, or care about weight; you get roughly twice the usable capacity per rated amp-hour and several times the cycle life. AGM if the RV lives on shore power and budget is tight. Comparison: flooded vs AGM vs lithium.

10. What size inverter do I need? Add up the watts of what you will run at the same time, then add 20–25% margin. A microwave alone usually needs 1,500–2,000 VA. A Victron MultiPlus combines inverter and shore charger in one box. Sizing guide: how to choose an RV inverter.

11. My Victron MultiPlus shows a blinking LED and shut off. What does it mean? A blinking LED is a pre-alarm; a solid one means the unit shut down. Low battery, overload, and temperature are the three common ones, and the pattern tells you which. Decode it with the Victron inverter fault codes guide.

12. Why does my solar controller show charging but the battery never fills? Usually the panels are too small for the daily load, the controller is set to the wrong battery profile, or a shunt was never installed so the "100%" you see is a guess. Check the controller's history in VictronConnect for daily yield, and confirm the profile matches your chemistry. Guide: best Victron MPPT for RV solar.

13. What fuse goes between the battery and the inverter? The inverter's manual specifies it; for a MultiPlus 12/3000 it is in the 400 A class, and smaller units use less. Use a MEGA, MIDI, or ANL fuse in a proper holder within a few inches of the battery positive. Chart: Victron cable, fuse, and busbar sizing.

Appliances

14. My 12 V compressor fridge stops cooling in the afternoon. Why? Two causes cover most cases: the condenser cannot shed heat because the vent is blocked or the vent fan has died, or the 12 V supply sags under load and the fridge's low-voltage cutoff trips. Test voltage at the fridge terminals while the compressor runs. Guide: fridge not cooling on 12 V.

15. Which rooftop A/C fits a Black Series HQ? The Dometic Penguin II 15,000 BTU is the common fit on the standard 14 x 14 in roof opening; confirm your roof cutout and the air distribution box style. Guide: Penguin II install.

16. Why does my electric awning stop halfway? Low 12 V at the motor, a failing remote battery, a bent arm, or a limit that needs resetting. Check the remote first; it is a $25.00 part. Guide: electric awning troubleshooting.

17. My propane/CO detector keeps chirping. Is it broken? Probably expired. Detectors have a service life printed on the back, and they chirp or flash at end of life. Replace it with a 12 V LP/CO detector; do not pull the fuse and leave the camper unprotected. Guide: how to replace an RV CO/propane detector.

Chassis, brakes, and hitch

18. Trailer brakes feel weak. Where do I start? Brake controller gain, then the 7-pin connection, then brake adjustment, then magnet condition. A corroded ground at the plug is the most common cause of weak or pulsing brakes. Guide: trailer brakes weak or grabbing.

19. How often should I repack trailer wheel bearings? Annually or every 10,000–12,000 miles for a trailer that sees dirt roads and water crossings. Follow the interval your hub manufacturer publishes. Use Timken bearings from the Brakes, Suspension, Tire & Wheels collection. Guide: how to repack trailer wheel bearings.

20. DO35 or DO45 coupling: which one do I need? Match the coupling to the trailer's rated gross mass: the DO35 is rated to 3.5 t and the DO45 to 4.5 t. Most HQ12–HQ19 campers use the DO35; heavier HQ21/HQ22T setups use the DO45. Guide: DO35 vs DO45.

21. What size trailer jack should I buy? Size to the trailer's tongue weight with margin, and check static versus dynamic ratings. The ARK XO350, XO500, and XO750 cover light to heavy off-road campers. Jacks are in the Towing & Hitch Essentials collection.

Doors, windows, and body

22. Why does my Black Series window not stay open? The gas struts have lost pressure. Measure the strut extended length and order the matching OEM window struts ($25.00 a pair). Guide: measure and replace window struts.

23. The key turns but the entrance door will not unlock. What is wrong? The cam inside the cylinder has broken or the latch spring has failed; either way the lock is replaced as a unit. Order the OEM Entrance Door Lock & Key or the 2019–2021 assembly for that model range. Guide: how to replace the entrance door lock.

24. Are Black Series parts covered by free shipping? Free standard shipping applies to eligible orders delivered in the contiguous United States, with no minimum order amount. It does not apply to Black Series generic replacement parts, or to oversized, freight, special-order, hazardous or remote-area orders. The product page and cart show the terms for each item, and any charge appears at checkout before you submit the order.

25. Do you offer service, not just parts? Yes. Seasonal Winterization ($183.20) and Spring Prep ($199.20), an Essential Annual Safety Service ($449.00), a Comprehensive Annual Service ($999.00), and an Off-Grid Power & Heating Service ($349.00). See Service & Maintenance.

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