Cariboocoot wrote: »
I hate to say "I told you so" but ...
It is most likely the uneven water flow causing the heater to cycle. However, your gas installation was somewhat less than perfect as I recall. Low gas pressure/volume would cause insufficient btu's. Too low will shut it down. Is the heater actually turning off and on, or is the flame just dying down?
And no pressure tank, or any other water system component, likes to be frozen. At least not with water in. Tanks are easily drained from a low point. Remember: gravity is your friend if you work with it.