Water Pump Pulsing or Running Constantly – Troubleshooting Guide

If your Mars caravan water pump keeps pulsing on and off, or runs constantly when no taps are open, it usually means the pump is trying to maintain pressure but can’t. The cause is often minor and fixable with a few simple checks.

This guide covers the most common reasons and what you can safely check yourself.

1. Understand What “Normal” Looks Like

In normal operation:

• The pump turns on when you open a tap.
• The pump runs steadily while water is flowing.
• The pump turns off shortly after you close the tap, once it reaches pressure.

If the pump keeps cycling on and off with all taps closed, or never stops at all, it’s trying to maintain pressure and something is affecting that.

2. Safety First

Before doing any hands-on checks:

• Make sure you’re on stable ground with the van secure and chocked.
• If working near wiring or the pump, consider switching off the 12V master when inspecting, and turn it back on only when testing.

If you smell burning, see scorched wiring, or feel unsure, stop and contact Mars support or a qualified repairer.

3. Common Causes of Pump Pulsing or Continuous Running

Typical causes include:

• Air in the lines or air being sucked into the suction side.
• Low water levels or tank pickups not submerged.
• Small leaks on the pressure side of the pump (after the pump).
• A tap or valve slightly open that you may not have noticed.
• Strainer or filter blockages restricting flow.
• Issues with the pump’s pressure switch or internal seals.

4. Step 1 – Check Tank Levels and Valves

• Confirm the fresh water tanks are not empty and have enough water.
• Make sure any tank isolation valves are open and correctly positioned for the tank you are using.
• If you have multiple tanks, verify you have selected a tank that actually contains water.

A pump trying to pull from an empty or partially isolated tank can cause pulsing and noise.

5. Step 2 – Look and Listen for Leaks

With the pump running or cycling and no taps open:

• Walk around the van and listen carefully near cupboards, under the sink and around the bathroom for the sound of running water or drips.
• Check inside cupboards and under the van for visible leaks or damp areas.
• Inspect connections on the pressure side of the pump (outlet and downstream pipes) for drips.

Even a small leak can cause the pump to lose pressure and cycle periodically.

6. Step 3 – Bleed Air from the Lines

Air trapped in the system can cause pulsing and spluttering:

• Turn the pump ON.
• Open the tap furthest from the pump fully on COLD and leave it running until the flow is smooth.
• Repeat on the HOT side (if you have a hot water system), allowing water to push air out.
• Then open other taps one at a time for a short period.

Once all taps have been bled, close them and see if the pump now stops and holds pressure.

7. Step 4 – Check the Pump Inlet Filter / Strainer

Many pumps have a small filter or strainer at the inlet:

• Turn off the pump and 12V master.
• Locate the inlet filter (usually a small clear or semi-clear bowl attached to the pump).
• Carefully remove it and:
  • Check for debris, sediment or restriction.
  • Rinse and clean as needed.
  • Reassemble, ensuring seals are seated and no air can be sucked in.

Air leaks on the suction side can cause the pump to draw air, leading to pulsing and loss of pressure.

8. Step 5 – Check All Taps and Toilets Are Fully Closed

Sometimes the cause is as simple as a tap not fully shut:

• Go through the van and check every tap (kitchen, bathroom, shower, external).
• Check any toilet flush or hand basin taps in the bathroom.
• Ensure external showers or wash points are turned off tightly.

Even a small trickle can make the pump cycle on and off.

9. Step 6 – Pressure Switch and Pump Wear (Advanced)

If you have:

• Confirmed tanks are full and valves are correct.
• Checked and cleaned the filter.
• Bleed the lines thoroughly.
• Found no leaks and all taps are fully closed.

Then the issue may be with the pump’s internal pressure switch, diaphragm or valves.

At this point, it’s recommended to:

• Contact Mars Campers support, or
• Have the pump inspected by a qualified caravan repairer or pump specialist.

10. When to Stop Using the Pump

Stop and seek professional help immediately if:

• You see significant leaks or water pooling inside the van.
• There are signs of electrical overheating (burning smell, melted wires or discolouration).
• The pump is very hot to touch and running continuously.

11. Information to Provide When Lodging a Ticket

When you contact Mars support or a repairer, it helps to include:

• Van model and VIN.
• Whether you have one or multiple tanks and which one you are using.
• A description of the symptoms:
  • “Pump pulses every 10–20 seconds with no taps open.”
  • “Pump runs constantly and never stops.”
  • “Water splutters and never runs smooth.”
• Photos of:
  • The pump and its plumbing connections.
  • The inlet filter/strainer.
  • Any visible leaks or damp areas.

Summary

A water pump that pulses or runs constantly is usually telling you that it cannot build or hold pressure. Common causes include air in the system, low tank levels, small leaks, blocked filters or pump wear.

By methodically checking tank levels, valves, leaks, airlocks and the pump filter, you can often solve the problem yourself – or at least gather clear information so Mars support or your repairer can help you quickly.