Main Vessel & PRV Kit 975102Kit contains: Expansion vessel Pressure relief valve (ErP variants may require different PRV. If this is the case choose vessel then PRV below separately). GasPart Vessel Kits make boiler pressure issue repairs as easy as possible. Good practice suggests replacing a PRV at the same time as a faulty vessel. A faulty vessel can cause damage to the PRV resulting in the boiler still showing a low pressure fault. Buying both together is simple and will