Hi Pressure cleaners

Try contacting the maker and explaining the ongoing problem.
If it's a "K*******" brand I am sure they will help.
I've had one for years, no problem apart from plastic wheels wearing out which I replaced with a solid axle and tyred steel wheels.

Cheers,
Barry

G'day Broodie
i got a Gernie(brand name) from bunnings,
model details are classic 125.2 great pressure good unit.

I have the "yellow one" but bought a model a bit more heavy duty, and it has a brass head.
If you read the fine print on the manufacturers website, some of the lower cost models are suppose to "have a rest" and are I think it was about 20 minutes maximum washing at a time with the alloy head models. Maybe ? that is contributing to your problem but as your only doing your car/van and boat your probably not running this long.
I bought the heavier duty model as I was living in North Queensland at the time and only had a rain water tank for water so had to wash the large house roof frequently and all the concreted areas so was advised by the dealer for the extra running time to get the brass head model, it was also the type we used at the minesite for prolonged Earth Moving Equipment washing.
Maybe take a break/have a coldie halfway through the job ?
The other "green one" is also good and can have problems too.
Best of luck.