Maintenance duties for a demand pump are simple to do, and pay off with trouble-free operation and independence from city-water hookups
Water pumps are found in every self-contained motorhome, and although they are designed to provide freedom from hookups, many people use them infrequently because they stay in full-hookup RV parks. But the fact remains that a demand water pump is integral to self-containment, and even if it is only used while on the road, maintenance is required to ensure it will work properly when called into action.
Regular maintenance is often overlooked, following the axiom “out of sight, out of mind.” But an annual maintenance check, and making corrections when needed, will ensure the ol’ pump will keep the water system flowing. While maintenance procedures often seem ominous, keeping tabs on a demand water pump is rather simple, and can be achieved by most Saturday mechanics. Following are a some guidelines and tips for proper maintenance and inspection.
It’s important to remove and clean the filter on the intake side of the water pump. Most water pumps arrive from the manufacturer with an attached filter to keep debris in the water tank from getting into the internal valves of the pump. The majority of these filters can be removed and separated in order to clean the screen. If you do not have a filter, purchase the appropriate model filter to fit your motorhome’s water pump. Inline filters are also available, if there is no room to fit the appropriate filter assembly directly on the pump.
Sanitizing the freshwater system, including the water pump, is one of the most commonly overlooked maintenance items. Some motorhomes sit for long periods of time allowing algae to accumulate in the water system; a buildup of algae in the water pump can damage the internal valves. Household bleach is commonly used for disinfecting water systems; however, a better solution is to use Purogene, which does not leave an aftertaste that lingers if the bleach is not flushed properly. Purogene is available at www.rvwaterfilterstore.com. Follow the manufacturer’s specified method for sanitizing the freshwater system.
Be sure to use a nontoxic antifreeze specifically designed for RV water systems; these will be safe for water pumps. There are service technicians who will winterize the motorhome using compressed air. The drawback to this method is the possibility of leaving a small amount of water in the pump that can freeze and result in a damaged valve assembly.
Even a simple diagnosis can save a weekend camping trip, so when the water isn’t flowing up to snuff always start by looking for a loose hose clamp or a kink in a hose. These simple checks might seem elementary, but they can help sort out the obvious first. Once they have been performed, it’s time to move on to more involved diagnoses. Listed below are some of the more common issues that you can expect to run into from time to time, and how to solve them before calling for expert advice.
The water pump runs, but doesn’t supply pressure to the system.
Be sure that there is ample water in the freshwater tank. After locating the water pump (for the above-mentioned check on the connections and hoses), make sure that the intake filter assembly is free of debris, which can restrict water flow. Confirm that any bypass valves used for winterizing have been returned to the normal position. When these valves are in a bypass position, water pumps may be unable to pull water from the storage tank.
Check battery voltage. Even though the motorhome may be plugged into shorepower, it’s not uncommon for problems to arise that may prevent the batteries from charging. Look for corrosion on the battery terminals that can contribute to diminishing voltage to the water pump, especially when there’s a long run of lighter-gauge wire between the batteries, the switch and the water pump. Minimum voltage should be roughly 11 volts DC at the pump, but voltage that low usually indicates a problem with the charging system or battery integrity.
Confirm that the water heater is filled, especially after winterization; this check is often overlooked when trying to pressurize the system with the water pump. After winterization, and before leaving home, attach a hose to the city water inlet and pressurize the system. It’s best to flush the water system of any residual antifreeze.
The freshwater tank fills and overflows when hooked to city water.
Most water pumps have a built-in check valve to prevent city water from entering the freshwater tank unless the valves are directed to do so. It’s not uncommon for the check valves to fail, as they are especially vulnerable to excess water pressure. Be sure to use an appropriate water pressure regulator, with no more than 50 psi measured at the city-water faucet. Certain model water pumps have replacement check valves available, and there are a number of aftermarket inline check valves that can be installed, as well.
The water pump won’t shut off.
It’s possible that air bubbles have formed in the water-delivery system. Check the intake hose and fittings from the water tank to the pump. Search for loose hose clamps, a kink in a hose to the pump, or a filter screen that’s partially clogged and restricting inadequate water supply or bubbles (which almost always come from the intake side of the pump). Check that the water filter is tightly screwed to the pump housing, as the plastic threads on both the filter and pump can be damaged by over-tightening or being cross-threaded at the factory (an all-too-common occurrence). Damaged threads will allow air bubbles in that don’t permit the pump to build outlet pressure and shut off. Special thread sealant may be required to repair damaged threads.
You hear the water pump cycling intermittently when not using the system.
Check for the obvious problems, such as a dripping faucet. Do not overlook the toilet, as the valve here can become defective and slowly fill the bowl over a period of time, causing intermittent cycling of the pump. Be sure that the water heater is full and that the air gap at the top of the tank is correct. Restoring the air gap can be accomplished simply by draining the hot-water tank, closing the drain valve and running the hot-water faucets (start with the faucet farthest from the hot-water tank first) until the sputtering is gone. It is not uncommon for the pressure to bleed from the intake to the discharge side of the pump through the internal valves, which would also cause intermittent cycling; it’s also possible that there’s a leak in the lines or fittings.
The pump runs, but will not prime.
Check for air leaks on the intake side between the water tank and the pump; make sure the O-ring in the filter strainer is not cracked or missing. Check hose clamps for integrity and, lastly, determine if the internal valve assembly is defective.
Basic repairs can be accomplished with a little knowledge and minimal tools. Two of the more common water pumps found in motorhomes are the SHURflo 2088 Series and the newer replacement model, 4008 Series. Below are some simple troubleshooting tips that apply to these pumps; the steps usually apply to other pumps used in motorhomes. Performing these tests just might save you a trip to the RV repair center.
If the water pump does not run, start the troubleshooting process by checking the fuse, typically marked in the fuse block. Using a multimeter or a simple 12-volt-DC test light, check for power on both sides of the fuse. Next, move to the water pump and test for voltage across the negative wire and the red positive wire leading to the pressure switch. If there is power to the positive side, check for power on the other side of the pressure switch. If there are 12 volts DC present on both wires, the motor is defective, provided there is an adequate ground. At this point, it’s more cost-effective to replace the water pump. If power is only present on one side of the pressure switch, it will need to be replaced.
There may be slight differences between models, but in many cases, the pressure switch and the diaphragm can be removed by taking out two screws.
If the pump runs but does not pressurize the water, remove the hose and strainer from the intake side of the water pump. Run the pump and put your thumb over the intake fitting and check for suction. If suction is present, the problem will typically be between the pump and the tank. If there is no suction, replace the head assembly or the valve assembly, both of which are available at Camping World, through www.amazon.com or at many RV dealers.
Replacing the head on a water pump is quite simple. The 4008 Series has six bolts, and the 2088 Series head is held in place by three bolts that protrude into the body of the motor assembly. Most motorhome demand water pumps have similar features. Remove the screws and carefully pry the head assembly away from the motor assembly. The motor shaft has a flat side, which is lined up with the corresponding flat side in the head assembly.
Pump problems can also be traced to low battery voltage when running under a load. Start by checking for proper voltage at the fuse. It can be no lower than 11 volts DC, under load, at the fuse. If the voltage is not adequate at the water pump (lower than at the fuse), install a water-pump latching relay designed specifically for water pumps. The latching relay utilizes a dedicated power source (larger-gauge wire) and the original wire to trip the relay internally. It is not uncommon for manufacturers to run inadequate-gauge wire over a long length, resulting in a voltage drop. Installing a latching relay will usually be necessary when installing a high-flow water pump.
If the water pump runs intermittently, check for voltage on both sides of the pressure switch. If the voltage cuts out between the two red pressure switch wires, replace the pressure switch assembly. If the voltage fluctuates at the pressure switch, the problem can be traced to the fuse or the battery. If the motor has continuous power but continues to be intermittent, replace the pump.
A common issue is a hammering sound when the pump is running. In many cases, this annoying trait can be traced to water lines that are too close to each other and are affected by the pulsing of water pressure from the pump. To fix, insulate the pipes with foam (normally used for water pipes and available at home centers) and tie them together to prevent the hammering noise. This is also good for insulating exposed pipes in cold weather. When the pump pulsates, the lines vibrate and, if they’re close enough to a wall, the sound can reverberate through the entire motorhome.
PEX (hard water lines) connected directly to the pump can also cause the hammering noise. Flexible hoses (usually 18 inches long and similar to water hoses) must be used to connect the PEX lines to the pump inlet and outlet barbs. Kits for this specific purpose are available at RV supply stores.
Replacing the water pump head assembly may stop the pulsing action, if it’s been determined that there are no other restrictions in the water line.
If the pump is bolted directly to a wood floor, its vibrations can reverberate through the floor structure. Consider mounting the pump on a secondary piece of wood and mount the wood to the floor via foam rubber blocks and contact adhesive, but not with screws, which will also transmit vibrations.
Various restrictions in the water lines, such as a kinked line or calcium buildup in the fixtures, can cause the water pump to short cycle when the showerhead or a faucet is wide open, as can a misadjusted pressure switch. Follow the manufacturer’s instructions exactly to adjust the pressure switch. Accumulator tanks, specifically designed for RVs, can be installed near the water pump to help mitigate short cycling, which could also be caused by inadequate water-line sizing. Make sure the pump is designed to be used with an accumulator tank.
If low water pressure at the shower head is experienced, the problems can be attributed to restrictions in the line, an inadequately sized water pump for the system, a worn valve assembly, low voltage, a defective vacuum breaker at the shower diverter, or simple debris blocking the shower head or faucet filter screen, which is easy to check and clean. A high-flow pump will often restore proper water pressure.
As one of the lifeblood systems in any self-contained motorhome, keeping the water flowing at good pressure enhances the experience – and curtails the stress of a poorly functioning demand pump.