Low Boy Water heater flowing backwards

Plumbing Forums

Help Support Plumbing Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Jmcc

New Member
Joined
Jul 31, 2018
Messages
4
Reaction score
0
Location
usa
Odd situation happening. New 20 gal low boy. Side outlet and inlets. The cold water is at the side bottom, of course. This is for a small one story office on a slab(rented). Lots of old faucets and other old water using fixtures that become points of concern (bldg is over 40 yrs old), so there is a master cut off in the mechanical room. The water supply is cut off every night. The old water heater was a top inlet/outlet and this didn't cause a problem. For various reasons, a new smaller WH with side inlets was installed. (the old WH couldn't be removed due to the fact that the previous owner built cabinets around and above it. go figure.)
So what happens is, when the master water valve is cut off, it appears that the full tank of water pushes the water in the tank back through the cold inlet pipes, when a faucet is turned on. You can feel the CW pipes get warm as the tank water flows back through the inlet piping. To me this shouldn't be possible. Like a hole in the bottom of a sealed water jug. You need the an opening at the top for the water to really flow. Is this remotely possible?
Now, If you take the new WH out of the loop by closing the CW inlet valve , and turning off the bldg. master valve, there is no flow at any faucet. Just like before.
 
If there is a return line connecting to the cold water and it circulates all nite the cold water out will heat up,there should be a check valve on the return line connecting to the cold water line feeding the cold going to the hot water heater, if you put a check valve above that connection. (Cold water) The hot water won't migrate past that check valve,we had this issue at work in a big dorm, during the summer the cold water would heat up,after putting the check valve on it stopped
 
If there is a return line connecting to the cold water and it circulates all nite the cold water out will heat up,there should be a check valve on the return line connecting to the cold water line feeding the cold going to the hot water heater, if you put a check valve above that connection. (Cold water) The hot water won't migrate past that check valve,we had this issue at work in a big dorm, during the summer the cold water would heat up,after putting the check valve on it stopped
Just want to clarify, just put a check valve on the cold feed to the hot water heater,the hot water won't migrate past that
 
Just want to clarify, just put a check valve on the cold feed to the hot water heater,the hot water won't migrate past that
I've looked into that. Is there a particular type or brand? the CW line is PEX.
 
Adding a check valve would definitely close the system if it’s not already. You’ll need an expansion tank and may need one now anyway.
 
I think watts,febco , Apollo, I prefer spring loaded but a wafer style is fine also,that's exactly how our systems are piped I also use IPS style with a union on one side and a male adapter on the other, this way you can change the check valve if needed
 
Last edited:
Adding a check valve would definitely close the system if it’s not already. You’ll need an expansion tank and may need one now anyway.
Right, I've read about Expansion tanks, but have never seen one installed in this area. It seems that one would be required if a check valve is present. BUT, A) no space for one in this install and B) I can almost guarantee the plumber has never installed one. Just not seen in this area.
But I'll ask anyway.
 
Right, I've read about Expansion tanks, but have never seen one installed in this area. It seems that one would be required if a check valve is present. BUT, A) no space for one in this install and B) I can almost guarantee the plumber has never installed one. Just not seen in this area.
But I'll ask anyway.
If you close the system with a check valve then it would be in your best interest to install some form of thermal expansion control and make sure your Temperature and Pressure Relief valve is operating.
 
Back
Top