About the Bosch PTOK Outdoor Freeze Protection Kit The Bosch PTOK Outdoor Freeze Protection Kit converts your Bosch Tankless Water Heater to an outdoor unit with complete freeze protection. The Bosch PTOK works with Bosch models GWH 640 ES GWH 715 ES GWH C 800 ES. The Bosch PTOK is suitable to protect your Bosch tankless hot water heater from climates down to approxiametly 5 degrees F (short term conditions only) yet will not protect appliance areas where routine climate is below freezing. Precautionary measures must be taken to ensure the plumbing around the applicance is protected as well. NOTE: If your tankless water heater is expected to experince below freezing temperatures for long periods of time it is recommended that your drain excess water from the unit. If a power outage occurs the heater should be drained. Damage due to freezing temperatures is not covered under the manufacturer waranty.[]