Pump may cycle against the closed V/V they often get damaged this way, Go to a plumb center and pick one up persomally take old with you they are normally flat but a o ring may be a best temp fix. If you are up north and temprature drops aroung 5 degrees it will run on frost protection.
Ok so I just got a Worcester Bosch 4000 boiler, It modulates, however their stat is junk and cant cope with metal walls, looses connection and is so slow I discarded, looked at tado, t6r honeywell, hive and nest none talk to boiler as wrong language of OT, the t6 r is tpi and boiler and rads set...