As long as you are using a suitable generator, then there should be no problem with this.
As a general rule, it is the generator supplier/manufacturer who are advise on which model is most suitable for use with pressure washers. A rule of thumb, a generator as a power supply must deliver at least 3 times the power of the high-pressure washer.
Generators can be put together in many different ways, and some have many safety systems and give precise and consistant outputs, while others vary a lot in use and have fewer protection functions against incorrect use. Some generators are intended for electronics that require precise current and voltage, while others are suitable for tools that load the generator differently during use.
Below are a couple of example use cases, so you can make a better informed decision on how to best use your washer:
Example 1; Master P80, a large and powerful high-pressure washer
This machine draws 2,800 watts. An generator that delivers a maximum output of 2,800 watts is too small, because generator manufacturers usually distinguish between maximum output and nominal output. In this case, we can use the Honda EU30si as an example: this unit is stated as 3,000 watts but has a nominal power (continuous power) of 2,800 watts. Thus, we can go ahead and say that everything is good so far. The next challenge arises when we read the user manual. In the manual we can read that maximum power should not be used for more than 30 minutes. This means that cleaning the house, which usually takes up a whole morning of washing, must be done in many rounds of less than 30 minutes, which can be difficult to keep track of.
Furthermore, we can read in the manual that people at higher altitudes must pay attention to the following: the carburettor must be adjusted when used at altitude, and even with an generator set up for use 1,200 meters above sea level, you must expect a power loss of at least 3.5% per 300 meters above sea level. Now the generator would be too small for anyone who had thought of washing somewhere like Geilo, or other popular mountainous areas. We accept that this is probably less of a problem in many of our markets than it is here in Norway, however it is still worth keeping in mind.
For those who are not going up into the mountains, and are still clinging to hope, the next thing to read is this: the total power output should not be exceeded. Unfortunately, this is what happens when you press the gun on a pressure washer. Then the engine starts and pulls 2-3 times the current upon start-up than it does under normal use. If, like many others, you wash a little, stop and wash again, the load, including these frequent starts, can quickly cause you to exceed the maximum that the generator is rated for. In the example above, we have used an expensive, high quality generator from a recognized manufacturer. This generator protects against misuse and withstands short-term overloads relatively well.
Example 2; a small high-pressure washer, for example a Go P40
This machine draws 1,700 watts and in this example we use a reasonable generator of 2,000 watts from an unknown brand. The problems mentioned above still apply, but on many affordable generators, there are major challenges with start-up. When the machine's power consumption increases upon startup, the unit chokes, as the lawnmower often does when mowing excessively tall grass. The motor cannot withstand enough load and dies. It could also be a blown fuse or worse; the voltage drops so much that the high-pressure washer switches off or, in the worst case, breaks. There is therefore a greater risk of the generator, the high-pressure washer or both parts being damaged.
A good, old rule of thumb when it comes to high-pressure washers and generators is that you should allow for 3 times the power consumption of the washer when looking at the power rating of the generator. Taking this into account, you should be confident that both the washer and the unit will perform well. The disadvantage of this rule is that it is expensive, and if the need is not there for such a powerful generator for other tasks than pressure washing, it becomes disproportionately expensive. Often the best thing to do is to talk to the distributor of the unit, tell them which model you will use and what the expected use is. A skilled tradesman or perhaps the manufacturer themselves will be able to give a qualified recommendation that will suit you, the unit and the high-pressure washer best.