Coleman pressure washer won't turn over.

If your pressure washer doesn't have an electric start, then leaving the switch in the on position would have done no harm. (It might have done no harm even if it does have electric start, but that depends.) Your most likely problem is gummy gas residue. Have you tried a spray starting aid like "instant start"? If you get some firing with that, but does not keep running, then your gas supply is clogged, probably at the needle valve that operates via a float. If it keeps running, then you may have cleared the clog already. In any case, be sure to use a gas preservative like "Sea Foam" or similar to prevent this headache in the future. If you found this useful, please vote. Thanks.

Hi and welcome to FixYa. I am Kelly

The switch being on should not make any difference on why your engine will not turn.

I suspect that your pressure pump is what is locked up vs the engine however, let's try the engine first.

Remove the spark plug and pour about 0.5 ounce of oil into the hole. Let it sit for about 20 mins.

Remove the recoil front cover just far enough to gain access to the flywheel.

After 20 minutes grab the OUTSIDE (not the fins) of the flywheel and rock it back and forth. Keep rocking it even as it starts to free up (if it does)

Once your sure it is free...
reinstall the recoil / front cover assy.

If after multiple attempts it is still locked up.

Gain access to water inlet fitting of the pressure pump so there are no other fittings / check vavles blocking access to the pump inlet. Add about 0.5 oz of oil to the water inlet hole.

wait 20 mins.....

Do the flywheel rocking routine above (front cover off of the engine)

It should free up pretty quickly.

Re-assemble and use.

Thanks for using FixYa!

Kelly