They will have to be recalibrated and maintained to ensure accuracy of readings.
Chapter 7 of the government's RHI announcement says
Maintenance requirements for meters
Periodic calibration of meters should be carried out by the manufacturer or by United Kingdom Accreditation Service (UKAS) accredited organisations working within the scope of National Accreditation of Measurement and Sampling (NAMAS) procedures. Other devices should also be appropriately calibrated, for example static pressure gauges and temperature sensors.
New or replacement units should be accompanied by a calibration certificate from the manufacturer. Evidence of calibrations of steam (or heat) flow meters, including the primary flow device, would be expected to be available if a site were audited.
The participant will need to ensure that these requirements have been satisfied as part of the RHI accreditation process and, where appropriate, provide evidence to Ofgem.