about your Marey Tankless Gas Fired Water Heater.
Due to the country wide harsh winter this year, Marey is seeing a disturbing instance of pressure bursts/freeze damage to their water heaters. This type of damage is not covered under their warranty. Marey Customer Service has been exploring options they can recommend to offset this type of damage. These options have not been tested and are not guaranteed to keep the units from freeze damage/pressure burst. However they have merit and are worth a try.
What is happening, at night when most people are asleep the water heaters are not being used, the frigid air is being drawn down the water heater's exhaust vent by other appliances such as a force air heating system as it is calling for combustion air during its cycling process. This frigid air is freezing the water pipes in the water heater (even though tankless there is still water in the heat exchanger pipes). As the water freezes it expands and burst or causes damage to the pipes.
For the GA5L, GA10L and GA16L units since these water heater use combustion air from the surrounding area and have only the natural rise venting here are the following options.
Option 1. Wrap a electric heat tape around the exhaust vent pipe (like a candy cane) to help warm the air as it is being sucked down the vent pipe to be uses as combustion air by the force air heater.
Option 2. Add a motorized damper and temperature controller.
If a motorized back draft damper were added to the exhaust section (Motorized Damper with End Switch) and fitted with a temperature control (RANCO ETC- 111000 120 - 240V Digital Cold Temperature Control). This would help to stop the cold from being suck down the pipe. However because these units are natural rise on the venting process there is not enough flow to open the damper thus the reason for the temperature control. When set at a specific temperature the controller would send power to the motorized damper and it would open. When the unit shuts down, the power would cut and the damper would close.
For the GA16L ETL units because they are direct vents a regular backdraft damper could be installed in the exhaust pipe. The temperature control is unnecessary because these units have a fan which would force the damper to open when the unit is active allowing the gases to go out the vent pipe.
If you are in an area with this extreme weather, I hope this email has reached you before you experience any damage. If you have had damage, contact Marey for options on repairs or consult your local radiator shop to see if they can re-flow lead free copper solder to close the burst and perform a pressure test (up to 150 psi) to be sure the patch will hold.
I hope this information has helped, if you have any questions, please contact me and I will be glad to try and help if possible.