pump motor works but no hot water comes out

Does any water come from the steam wand while the pump is running? The pump may be dry and unable to prime itself, and the steam you're seeing is just the remaining water in the boiler evaporating. If no water comes from the steam wand then you may need to prime the pump by forcing water into it with a turkey baster or other similar implement while it is running. As soon as it starts to suck the water through reconnect it to the water tank and let it run for a while to ensure the boiler is full.

If you can get water to flow from the steam wand but none comes from the bare brew head then you probably have a clog in the brew head valve. If water will flow from the brew head when the portafilter is off, but none flows when it is in place (with or without coffee) then your pump is probably failing and will need to be replaced.