This can be a jammed or faulty pump.
It's the most common cause so you need to check it first.
The machine won't heat while the light is lit.
Unplug the appliance.
At the bottom rear is a bulged container.
Lever this open, it hinges out, then lift the top off of it.
Take the hoses off, blow up them to ensure they are clean and clear.
Take the pump out.
Remove any debris in the pump.
Clean out the pump reservoir.
Check the float hasn't stuck.
Take the condenser out at the front.
Clean it out thoroughly.
Reach into the condenser chamber as far as you can and scoop out any fluff.
Reassemble the appliance and try it again.
Check it out, see what you find and get back to me if you need more help.
Hope this helps