I have a grant vortex boiler ( combi) type, I have replaced the old one when that was leaking, a month ago. Now I find that the new one is now leaking. Does anyone have any ideals please

What is the water pressure and what is the pressure rating of the PRV.

Shut off the boiler & the incoming water. Drop the boiler pressure to zero then check the pressure in the expansion tank. For most houses the tank pressure should be 12-15 psig. If you have no pressure, the bladder has probably failed.

A leaking PRV (Pressure Reducing Valve), or a leaking T&P (Temperature and Pressure) relief valve?

What's the house PSI ? I wonder along with Harold, Are we talking PRV valve into the house or are we talking about the boiler T&Pn valve? Back to you, Tom

A boiler doesn't normally have a T&P valve, strictly pressure & usually set for 30#. Yes, it could be a reducing valve but I've never seen one leak except at a joint.

Tony636,
What pressure is the gauge on the boiler showing?