Could be a few different problems, does the central heating demand light come on ? ( a (LED) light on the boiler) if it does then the room thermostat is calling for heat and the problem is with the boiler.
If the demand light to not come on, then its possible the room thermostat is faulty.
The easiest way to check this is to does the room thermostat click when turned up ? if so it's probably ok.
If it does not click, you need a new stat - temporarily you can link out the room thermostat either at the boiler or at the thermostat,
TURN OFF ELECTRICITY SUPPLY TO BOILER
The boiler instructions will show where the room thermostat is connected(normally a terminal blcok next to the PCB). Disconnect these two wires and form a link with a small bit of wire and connect to where the stat should be.
Or take front of the room stat and link the mains LIVE IN to the SWITCH LIVE
if all ok with thermostat etc. then's there's probably a fault on the PCB
Given the situation described, before engaing in a massively expensive repair cycle, consider the simple options first.
Is the pump actually running. If it is located low in the system it is possible that a collection of debris has settled in the pump and stopped it turning. Some pumps have a screwdriver slot in the end of the shaft, you may have to pull off a snap on cover to see it. If there is one try turning the shaft witha screwdriver. This should start the pump turning.
Next, if that doesnt work, check that any changeover valve - if you have a fully pumped system, is actually changing over when you demand heat. there will be a lever on the side with three positions. This lever moves to divert hot water from Water only/ Heat only / Both. Of course if you have a gravity fed hot water system the valve will not be there, and I would put my money on the pump. If it doesnt have a slot in the shaft try tapping it hard with a block of wood - not a steel hammer.
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