Ext version tested:
4.0.2

Code to reproduce
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
    <title>Chart bug demo</title>
 
    <link rel="stylesheet" type="text/css" href="extjs/resources/css/ext-sandbox.css">
    
    <script type="text/javascript" src="extjs/ext-all.js"></script>
    <script type="text/javascript">
        Ext.onReady(function () {
            var chart = new Ext.chart.Chart({
                renderTo: Ext.getBody(),
                width: 800,
                height: 600,
                animate: true,
                store: Ext.create('Ext.data.Store', {
                    fields : ['name', 'data1', 'data2', 'data3'],
                    data : [
                        {name: 'Jan', data1: 0, data2: 0, data3: 0},
                        {name: 'Feb', data1: 0, data2: 0, data3: 0},
                        {name: 'Mar', data1: 0, data2: 0, data3: 0},
                        {name: 'Apr', data1: 0, data2: 0, data3: 0}
                    ]
                }),
                renderTo: Ext.getBody(),
                shadow: true,
                theme: 'Category1',
                legend: {
                    position: 'right'
                },
                axes: [{
                    type: 'Numeric',
                    minimum: 0,
                    position: 'left',
                    fields: ['data1', 'data2', 'data3'],
                    title: 'Number of Hits',
                    grid: {
                        odd: {
                            opacity: 1,
                            fill: '#ddd',
                            stroke: '#bbb',
                            'stroke-width': 0.5
                        }
                    }
                }, {
                    type: 'Category',
                    position: 'bottom',
                    fields: ['name'],
                    title: 'Month of the Year'
                }],
                series: [{
                    type: 'line',
                    highlight: {
                        size: 7,
                        radius: 7
                    },
                    axis: 'left',
                    xField: 'name',
                    yField: 'data1',
                    markerCfg: {
                        type: 'cross',
                        size: 4,
                        radius: 4,
                        'stroke-width': 0
                    }
                }, {
                    type: 'line',
                    highlight: {
                        size: 7,
                        radius: 7
                    },
                    axis: 'left',
                    fill: true,
                    xField: 'name',
                    yField: 'data3',
                    markerCfg: {
                        type: 'circle',
                        size: 4,
                        radius: 4,
                        'stroke-width': 0
                    }
                }]
            });
        });
    </script>
</head>
<body></body>
</html>
If you will change at least one value to 1 in data left axis will be rendered.

How to fix
Chart isn't rendered because Ext4.chart.axis.Numeric calcEnds thinks that there is no data.

I added this code at the end of this private method:
Code:
            if ((out.steps == 0) && isNaN(out.to) && store.getCount() > 0) {
                out.steps = 1;
                out.to = 100;
                out.step = 100;
                out.power = 2;
            }