Boiler ignite light on but no hot water

It could be diverter valve stack in one position if it's combi boiler. Call manufacturers help line or customer service. Ask what it can be and how to rectify the problem. They might be able to guide you through via phone. If not ask how much it will cost you to invite their approved gas safe registered engineer. They are there to help you.

A couple of things instantly spring to mind. It could be the diverted valve (head). Or I'd be looking at the plate heat exchanger that could be blocked and need a good clean out.