Success! After a long battle, we finally figured out the problem. It turns out, there was a bad check valve, near the recirculating pump that allowed the cold water to get into the system. the same check valve failed on both systems. We opened it up, and both of them were encrusted with calcium deposits and hard water debris not letting the valve close. Just for future reference to anybody with a similar problem here is how we tackled it: -We checked the dip tubes on both hot water heaters , and both of them were fine. -next, my plumbers isolated the hot water heater to make sure the heater was running properly. all checked out fine. -We turned off the radiant heat systems and bypassed them with the built-in valves. -My plumbers opened up each shower fixture and closed off the water valves to take those out of the equation. the hot water still ran cold. - Next, the plumbers removed the recirculating pump and checked the system. the water still ran cold. at this point it had to be the check valves, since nothing else would cause the cold water to come back into the system. - The plumbers then starting removing the check valves beginning with the one near the recirculating pump and discovered the broken valve. If this still didn't work, they would've kept going to check every check valve in the system(three total). the plumbers installed a temperature gauge to be able to see the change in water temperature. now the temperature holds solid and 120� when the hot water is turned on. I can't wait to take a piping hot long shower. Below is a picture of the plumbing system if you were curious. Two water heaters, one for each unit with the radiant heat manifolds. Radiant heat system by Warmfloors, Napa Ca Installation by AG Quality Plumbing San Francisco, CA(the best plumbers in San Francisco by far) Thanks all! Here is a link that might be useful:

There's an overflow-tube inside the tank. If the float is set too high, the water-level will trickle over the top and run into the bowl while the valve keeps trying to fill and raise the float. Float-stopped water level should be 1/2" to 1" of so below the top so it doesn't do that. Sometimes the float will come out of adjustment over time and the water level will sneak up on you.

Sorry for delay and thank you for your interest brickeyee. Aprilaire Humidifier model 760 flow through system. When HVAC was here in September doing fall furnace check he installed a new AA feeder tub ("NP OTP" on bill), saying the old rubber tube may have weakened and splayed at its end over the years and pose a water leak risk. He also put in a new water panel and #35 pad. There was no discussion of the Solenoid valve assembly nor of the water inlet orifice. No problem was noted on testing the humidifier except for water leakage from the gas water heater branch supply: the "saddle" valve controlling hot water supply to the dedicated humidifier line leaked. All was turned off until further investigation of this saddle valve. Below are pictures of the water valve above the gas water heater: some say it is a saddle valve (which, as all or nothing" is not allowed I gather) and others, including the company's plumber say it is a turn valve. The company plumber tightened up the nut a bit on Friday and the leak seemed to stop. The system was turned on for test, but after the plumber left I noted the continuous water running to the humidifier, heard it spraying into the box and saw the constant stream from the outlet to the sump pump so I turned it all off again. Here are key points Aprilaire owner's manual makes on the 700 models: "The correct water flow is determined by an orifice equipped with each drain type humidifier. When the humidifier is operating, there will be a small, steady stream of water to drain, which flushes away most of the trouble-causing minerals. Do not use the saddle valve to regulate the water flow. It is designed to be completely open or closed." Here are some photos-sorry can't seem to resize them on PB: http://www.aprilaire.com/themes/aa/en/manuals/Owners_%20Manua_Model_400_%20500_%20600_%20700_10006899.pdf to be completely open or closed." Basically, the Aprilaire Humidifier looks like this and has separate humidistat on return. Thanks for any advice.

I also think it looks like canker. The organisms that cause canker are around all the time and enter through the "skin" of a plant when it is injured, cold can cause injury so that spring is a common time to see canker damage. If the canker encircles the stem, all nutrients are cut off and the stem above the canker dies. If the canker does not encircles the stem, then it should recover. I agree that pith will show if the stem is alive or not, but you must cut off the stem off to see the pith, it is that corky stuff in the middle of a stem, but now the cane is dead for sure. You can check for life under the bark with the scratch test, and as long as there is green under the brown, there is hope. It can be false hope because the stem could have died below where you scraped and the top of the stem as yet to die, that's why a stem can continue to produce foliage for a short time even after it is dead lower down. In my experience, you can kill a weak plant by pruning off all the canker damaged stems, when if you just left it alone, it be would be ok. You can always prune the stem later if it dies, If it is a vigorous plant then pruning it won't hurt, do clean your cutters after each cut. You do not want to spread it to healthy wood.