Shower Trouble

Does not  sound normal to me..

Does the water to the sink and basin behave in the same way?

Sounds like a pressure reducing set up as Aquaroll filled manually or automatically would work the same.

One thought is, if an in the barrel pump, is it floating up and pulling in air instead of cold water.  Or if a water uptake and onboard pump, the same scenario is even more likely as less weight to keep things submerged.

If this may be happening, fix the pump/water uptake hose to something rigid to ensure it stays at the bottom.  We have a wide plastic pipe that ours passes through.

could be but if it is likes ours the pump in inside the caravan (all that goes into the aquaroll is a pipe), in which case it may be the pressure dial needs adjusting to maintain an even pressure?

Ours is onboard, just the water uptake in the Aquaroll, but we have an accumulator  just beside the pump that evens out the flow of the water, so no adjustment of pressure switch needed.

I would like the answer to whether all taps are affected by this, or just the shower.  It sounds like there is some restriction in the cold water pipework that cuts down the flow of cold temporarily,  and if it is just the shower affected then the pipe to it is the place to look.

Could be debris caught up at a joint or bend, a kink in the pipe, a fixing clip that is compressing the pipe, though you would think that would produce a permanent restriction rather than something that comes and goes.

Another thought is that there may be some valve in the cold feed that is sticking or behaving strangely, not familiar with the plumbing in an Elddis, or indeed with the direct water system as we use the via Aquaroll method.

Yes it is inside the caravan, all that goes outside is the attachment for attaching it to the inlet and a blue hose with a filter at the end that goes into the aquaroll. There is a dial inside to regulate the pump

However because there is no weight to it it does curl up sometimes as Kj says

With an onboard tank like we have, you need an onboard pump. It fills the tank, and can be set to use from either tank or Aquaroll.

I like it better than the in the barrel one we had in our previous van,  much more powerful, sturdier, and does not mind running dry.

Ours is very quiet now that I have sorted out the pipework!

I think most Swift Group vans now use an onboard pump.

Wouldn't waste any more time on the problem.  A 2020 caravan, back to the dealer to sort out under guarantee.