I have had my steamer for years and love it, but lately it wouldn't steam so my husband took it apart and did what was suggested. Now if just steams all the time without having the button on the handle depressed.
It sounds like your husband has put this back together wrong or did not follow the complete instructions in the video he watched. I would suggest that it be taken apart again and looked it. It sounds like there id an issue with something blocking the switch so it stays on all the time. Check the contacts and make sure you can press the switches in both directions before putting it back together.
You say you have been using your steamer for years so had it ever been cleaned before? I mean cleaned of lime deposits? Are you using tap water or distilled water?
I always use distilled water and try to give it a good cleaning every 6 months because I use mine a lot.
Since your husband cleaned it do you know if he removed a lot of deposits?
It's possible that some of the scale got trapped in the area around the button and this may be keeping the button from operating correctly.
I have sprayed a little bit of WD-40 around the button and it seems to keep it working better.
There are some suggestions that others have tried so take a look to wee if you need to redo your job just in case there was scale left or something did not 'seat' just right.
This site has a lot of suggestions - some may be the reverse of what you tried so take a look - lot of info at the bottom of the page too.