14/05/2025

How to Prime a Caravan or Motorhome Water System Properly

So, you’ve just got to the site. The kettle’s ready, the sunset’s putting on a show—and then you turn the tap and… nothing. Maybe a dribble. Maybe a worrying buzz from the pump. Either way, not exactly the start you were hoping for.

Whether it’s your first tour or your fiftieth, priming the water system in your caravan or motorhome is one of those “small jobs” that’s oddly easy to get wrong—but incredibly satisfying when you get it right.

We actually made a video on this a while ago (watch it here) and it’s still one of the most-viewed guides we’ve ever posted. Why? Because it’s one of those tasks nobody really teaches you properly—until something goes wrong.

Let’s fix that.

What does “priming the system” actually mean?

In plain English? It means getting water from your tank through to your taps.

But more specifically, priming is about:

Getting water flowing smoothly through the pump

Clearing out any trapped air in the system

Making sure your boiler (if you have one) is filling correctly

Checking for leaks or loose connections before you need the loo at 2am

Think of it like bleeding a radiator crossed with setting up a fish tank—with fewer bubbles and more swearing if it goes wrong.

When do you need to prime it?

Honestly, more often than you think. Here’s when you’ll usually need to do it:

After draining down for winter

When using your caravan/motorhome for the first time in a while

After replacing a pump, tap or pipe

When air’s been introduced into the system (accidentally or otherwise)

So if your tourer’s been sat in storage for a couple of months, priming the system isn’t just a good idea—it’s non-negotiable.

Alright then—how do you actually do it?

Here’s the thing: every setup’s a little different. But whether you’ve got a Swift motorhome with an onboard tank or a Bailey caravan with an Aquaroll and a submersible pump, the principles are the same.

Here’s a step-by-step you can count on.

1. Fill your fresh water container or onboard tank

Let’s start simple. Whether it’s an Aquaroll or an inbuilt tank, make sure it’s full—or at least got enough in it for the system to draw from. And yes, make sure it’s clean (you’d be amazed how quickly biofilm builds up in a neglected container).

2. Connect the pump and switch it on

This might be an external submersible (like Truma or Whale) or a fixed internal one. Plug it in securely and turn on the water pump from your main control panel or switch.

If you’re using an onboard tank, make sure any isolation valves are open—otherwise your pump will just sit there humming to itself.

3. Open all taps—starting with cold

Now here’s the key: open every tap fully, one at a time. Kitchen, bathroom, shower—don’t forget the shower!

Start with cold water only. Why? Because cold flows direct from the tank and pump. Opening the hot side first can cause backpressure and more airlocks. You’ll usually hear the pump labouring a bit at first, maybe some spluttering and hissing—totally normal.

Let each tap run until the water flows smoothly, without bubbles or spurts. You’re pushing air out of the system, bit by bit.

4. Then do the same with the hot

Once cold is sorted, repeat the process with the hot taps.

This is where your water heater (usually a Truma or Alde unit) comes into play. When you open the hot tap, you’re drawing cold water into the boiler and forcing air out. Again, expect gurgling, maybe even a pause before anything happens.

Let it run until the flow is smooth and consistent. If your boiler has a pressure relief valve, check it’s not dribbling or hissing. If it is, it might just need reseating.

5. Check for leaks

Sounds obvious, but after every prime, take a moment to check under sinks, around pipe joins, and beneath the van (in case of a failed drain point). Catching a leak early saves a lot of grief later.

Common hiccups (and what to do about them)

No water at all?

Check the pump’s getting power

Confirm any isolation or drain valves are closed

Double-check the pipework isn’t kinked or blocked

Pump runs constantly?

You may still have air in the system—run the taps again

There could be a minor leak the pump’s trying to compensate for

Some pressure switch systems just need a tweak—refer to your manual

Water sputtering or weak flow?

Airlocks are likely—leave the tap open a bit longer

Check filters in the pump (they clog more often than people think)

Onboard tanks? Make sure your tank’s vent isn’t blocked

Want to watch it done?

This might be a good time to bookmark this video guide—we show the full step-by-step, and it’s been a lifesaver for loads of first-time tourers and even a few seasoned pros.

Or weve embedded it here:

Quick tip: Priming gets easier with habit

You know what? The more you do it, the more second nature it becomes. It’s just like hitching up or levelling out—you stop overthinking it after a while.

At Kimberley, we always recommend re-priming the system after servicing or extended storage. If you’re booking a full motorhome or caravan service, our team can make sure the water system is ready to go before you even hitch up.

Final thoughts

Priming your water system might not be glamorous, but it’s a must-do—and once you’ve nailed it, you’ll wonder why it ever felt confusing.

Give it time, don’t rush, and remember: spluttering taps are just your system’s way of saying “hold on, I’m getting there.”

And hey—if you’re still unsure, swing by a Kimberley branch or check out our YouTube video for the full walkthrough. Because a working water system? That’s where proper holidays begin.