1. First Method

you have to assign null or empty string here

this.searchValue = null;
//or
this.searchValue=" ";

Working Plunker

because no event is being fired from angular change detection. so you have to assign some value either null or string with space

2. Second Method

• use of [(ngModel)] it should work with ngModel.

why ?

because as you did binding with value attribute which is only property binding not event binding. so
angular doesn’t run change detection because no event relevant to Angular is fired. If you bind to an event then Angular runs change detection and the binding works and value should be changes.

see working example of same with ngModel

Working Example with ngModel