Do you have a combi boiler or do you have a cylinder?
do you have a room stat?
Ok, can you turn on the heating and tell me what happens - pump, fan, etc
What is the pressure gauge reading?
When the heating is activated then the pump should start first and the fire up the boiler via the divertor valve.
Can you check power to the pump - or see if it is stuck by checking the screw in the centre?
Centre of the pump - a plug with a slot, it unscrews and then you can see if the insides are spinning
But not when you turn on the heating?
Do you have any fault lights or codes?
Do you have the make and model?
There could be a number of causes of this fault, including a faulty temp sensor, blocked heat exchanger or faulty pump.
The hot water will use a separate heat exchanger, and I would be inclined to start looking at the CH heat exchanger and temp sensor, and work from there if the CH outlet pipe is not hot.
With this being a gas boiler you will need a gas safe engineer to strip down the boiler and recommission it, please let me know if you would like me to recommend a local engineer.
Do you require any further assistance?