I had a new boiler etc including a new Central Heating Motorised Valve fitted about 6 months ago. This has now started to bang and whirl very loudly when the water/heating comes on. I recently fitted a new shower could that have affected it?
Turn of the electricity to the complete heating/hot water installation - boiler will go out - the indicator on the side of the valve should go to W.
Check the valve is installed the correct way round. Port AB to Pump; Port A to radiators; Port B to Cylinder. (ports are labelled on the brass T-piece)
There is a lever on the end of the valve which slides in a slot. Push this lever over. You should feel resistance as you are opening the valve against a spring. Release the lever and it should move back.
If the lever is loose, the valve is stuck in the heating open position. Remove the actuator (button on side) and check the spindle of the valve can rotate easily (not a full rotation, about 20 degrees).