Hi,

I moved from the eastern US to Las Vegas a few years ago, so I am unfamiliar with a "dual hydronic" heating system, which I think is what they call this thing...

Basically, my hot water heater doubles as my heating system in that there is a hot water outlet that goes up into the ceiling and must run through some coils and fans or something, which allows me to blow warm air throughout my condo.

Anyway, my hot water heater died a few months ago and I had it replaced. Hot water was flowing fine to my faucets before the new install ever since, but about a week ago I finally turned on my heating system for the first time. That seemed to work fine also. I discovered the problem the next morning when I got in the shower and the water was barely warm...I thought the hot water heater went out and the water had just cooled over night, but when I checked it, it was fine -- for some reason the hot water just isn't making it directly through my faucets after running the heating system.

In doing some tests, I found that:

1) If I completely shut the valves that go to the heating system, then hot water will make its way to my faucets again, but then I can't run my heating system!

2) If I open the heating system valves AND the heating system is actually RUNNING, then it also seems like hot water makes it to my faucets.

3) HOWEVER, if I have the valves open to the heating system but the system is NOT running, then the hot water does not make it to my faucets... it appears that the pipes to the heating system are the path of least resistance when it's not running, so my hot water is mostly just running through there instead of going to my faucets (at least I think that must be what is happening).

4) Keep in mind, before the new hot water heater install, everything was the same in that the valves were open to the heating system loop but the heating system was not running, but I was still getting hot water to the faucets just fine.

I've read (after I had the hot water heater replaced) that it is very important for these systems to "bleed them" when installing a new water heater. As far as I know, the plumber that replaced mine did not bleed anything having to do with the heating system. Could that have created this issue? Is it something I can fix myself, if that is the case? Basically the only thing that changed was I got a new hot water heater installed, so something in that process seems to have triggered cold water getting drawn into the hot water faucet lines...whether cold is running backwards through the heating loop now or is somehow getting dumped into the top of the water heater as I try to use hot water, I don't know, but somehow cold water is making its way to the hot water lines.

For additional information, it does NOT look like there are actually completely separate, isolated pipes going to the heating system. The hot goes out of the top of the water heater and there is a split--one goes into the wall (and to my faucets, etc. I guess) and one runs up into the ceiling to the heating system. Same with the cold side -- the pipe from the heating system runs down and connects into/meets with the cold water supply that connects to the cool water input to the water heater.

its hard to say but it sounds like rather than not getting hot water, what is happening is that the cold is somehow getting into the hot side you get warm rather than hot water.

Yes, that is exactly what appears to be happening.

My confusion is that it was not happening before the new water heater install, but now it is. I called the plumbing service and they said it sounded like a bad check valve. It does sound like that, but I'm wondering why it occurred immediately after the water heater was installed and if failure to bleed the system properly in a dual hydronic setup like this could have triggered it.

It seems that now, whenever the heating system is not running, the cold water supply is of higher pressure than that heating loop so the cold is pushing that way...as soon as I open the hot water valve, a bit of hot water is coming out of the water heater but that cold water is pushing its way in along with it whereas before, something (check valve, I guess) was preventing this.

I have read that it is of paramount importance to properly bleed the air out of the dual hydronic when replacing the water heater, but I can't find out WHY or WHAT RESULTS if you don't. More to the point, I'm wondering if my exact scenario is what may happen when the proper bleeding procedure is not done...that, other than extreme, extreme coincidence is the only thing I can come up with at the moment.

-Doug

It sounds like a check valve is not holding. Could be due to scale build up. I have installed 100s of systems like this with tank type and tankless water heaters. And 90% of the time it is the check valve when water temp is not the same out of faucets as out of the heater

Thanks -- that's pretty much what I've been hearing from everyone so far.

-Doug

Another thought is that the circulating line needs to be throttled back to allow it to gain more heat. Adjust your ball valve carefully to accomplish this. Be sure not to close it off completely though. Good luck.