Elström

[elionaral]

I bought upright piano called Elström 100 years old. I am a pianist and use it only for practicing being abroad.
I have a problem : last month 3-4 stucked keys
Maybe change the technician? or it will happen all the time
What is the best way to repair it?

[indianajo]

Your technician should quote his estimate of repairing the problem, if you point it out to him.
Many will not touch this problem.
I you are authorized to work on this piano, you may look at it carefully.  Take the covers off.  Is the sticking happening at the key or at the hammer, or at the whippen?
Sometimes old pianos have had a bit of moisture at some point and something warped.  
Sometimes old pianos have deteriorated felt.  This is more of a problem, as fixing one by replacing felt may not prevent another key from going sticky in a few months or weeks.  
If a key is sticking against the side of another, they are easily removed and the sides sanded down with a machine.  The bar over the keys unscrews after the front is out for tuning.  Keep your screws and parts in a zip lock baggie, you may not find anything similar.  Maybe somebody spilled a drink at one point, only a couple of keys were warped, and the repair could be permanent. 
If a whippen or hammer is sticking, more analysis is required.  I suggest it requires permanent commitment to a piano to unscrew the hammer from the action and go into repairing this.  In my neighborhood, entire new upright actions are available in old pianos at Salvation Army for $40 to $100.  A premium Baldwin Acrosonic spinnet went for $40 two weeks ago. It has a scratch on the case.  A middle market Story & Clark 40" (slightly slow action) with a perfect case & bench is going for $75, unless after two months the price will halve.
The cost of moving the 100 year old upright out and another in would cost more than one of those.  Plus in many locations there is a disposal fee for old uprights.  So looking to see if it is a simple key rub which can be repaired by removing & sanding is certainly worth it.
Best of luck.

[hfmadopter]

I agree with indianajo in that something could be rubbing. At least check the most common problem first, which would be hammers rubbing together from a warped shanks or a loose screw. Often you can just loosen the knuckle mounting screw and slightly shift the shank over and re-tighten. It's a 0 dollar repair that once upon a time was included in a general tuning.