Backwash while pump is on

[astargel]

I have an AG pool with a 1.5 HP sand filter/pump.
I went to backwash the pump and forgot to turn off the pump first. Now when I flip the on/off switch, it powers on and hums, but nothing happens. This has occured before, but it "magically" started working again.
Does anyone know the trick to fix this?
Thanks

[Poconos]

There is no relation between what you did with the filter and the pump not starting. Just coincidence. Since the motor has done this before it is probably just dirty starter switch contacts. Wish I could find the thread that described this stuff in detail but I can't. So....there is a centrifugal switch usually on the back end of the motor under the cover where the wires go in. There are a set of electrical contacts that are closed when the motor is stopped, and open when it comes up to speed. This switch allows a starting winding to be powered and then disconnected when up to speed. If the contacts are dirty then the starting winding is off and you will hear a low level hum because the running winding is powered. Sometimes lightly smacking the motor housing with a 2x4 will jostle the contacts enough to make contact and it will start. You need to clean them. The contact material is soft, usually silver, and gets pitted over time. Get some 400 grit wet-or-dry sandpaper (auto store) and cut a strip of paper and slip it between the contacts and lightly dress them. If you can get a thin, flat file in there all the better. You just need to kind of polish the contacts, not grind away.
Let us now how you make out.
Al

(ajs-1)

[astargel]

AL!!!! You are a GOD SEND! That's all it was
ROCK ON! Thanks so very much for your help!!!

[Poconos]

I wonder how many new pumps are sold to solve these relatively simple problems.
Glad I could help.
Al
BTW: About the only thing that could happen when changing valve positions while the pump is running is to lift the spider gasket out of its channel in the valve assembly. Then you will have leak paths between ports that should be isolated. Solution....new gasket.