Handling error in http calls in ionic 2

In my Ionic2 app, I have a service which handles all http requests. I have an alert controller when any error occurs in http call. On button click in this alert I want to run that call again. I am able to do it right now. The problem is response is not resolved to page from which function was called.

Code in service:

loadCity(){
return new Promise(resolve => {
this.http.get(url).map(res=>res.json())
.subscribe(data => {resolve(data)},
err => { this.showAlert(err); }
});
}

showAlert(err: any){
// code for alert controller, I am only writing handler of alert 
//controller refresh button
handler => {this.loadCity();}
}

Code in CityPage

showCity(){
this.cityService.loadCity()
.then(data => {//process data});
}

Handler is calling function again but this time promise is not resolved to CityPage showCity() function.