The Tower RFWRT only controls the heating side. The hot water (I assume the 28i is the Combi version) is controlled by the boiler.
Comments below assume that the system has been working correctly and has not been tampered with.
If it is a new installation and never worked or been tampered with, call in a heating engineer.
Comments:
Assuming that your hot water is working, the issue is on the CH control side.
You can test the RF connection between the thermostat and the receiver (refer to the Manufacturers Instructions) if that is working look at the zone valve and check that the end switch is working. If the end switch is working and the RF connection is ok the boiler will fire on a call for heat. If so and no heat is entering the system check that the valve is actually opening.
If the RF connection is not working, it seems wasteful, but it is probably easier and cheaper to just change the receiver and RF thermostat units. a replacement Tower unit is around £40
If you don’t feel competent to check out the valve and end switch ( the valve will be 240v) call in a heating engineer. Equally replacing the Tower receiver will involve a 240v connection
If RF connection is ok and the zone valve is functioning then the issue is within the boiler and you will need a Gas Safe Registered engineer to resolve it ( it is probably an internal boiler valve issue)