37 Mounting, installation, maintenance and repair of electrical, oil- or gas- operated heating, cooking, drying and ventilation apparatus, namely, room heaters, hot water boilers, flow heaters, storage water heaters, closed circuit heaters, combined central heating and service water heaters, heat exchangers, heating boilers, gas burners, oil burners, heat accumulating apparatus, central heating apparatus, wall-mounted gas heating apparatus, wall-mounted gas hot water apparatus, water heaters, bath water heaters, wall boilers, and tankless gas water heaters operated with gas and instantaneous water heaters operated with gas and parts of the aforesaid goods