I have a single-zone hyrdonic system which uses a dedicated 50-gal. AO Smith natural gas water heater (I know, I know, probably not approved for space heating) feeding PEX tubing set in a structural concrete slab. There is a Honeywell RA832A controlling the circulator.

Before turning the system on last week I decided to drain a gallon or so of water out the bottom of the water tank, hopefully to capture any sediment. What I got was a pailful of cloudy, yellowish, and very smelly (sulpher+dog pee) water. I decided to pull a second gallon and got the same.

I am sure water in the system stagnated over the summer, but is this a sign of something bad?

Incidentally, the system is working fine in SPITE of the fact that it ran all last winter with the cold water supply line valve (make-up water) CLOSED. (This past May on this forum, we concluded that "in general" this valve should be OPEN, which it has been since then!)

With the system idle at noon today, supply to floor was running at 95 deg.F. at pressure of 15, and return was at 80 deg. F. I think while running the supply to floor runs at about 115.

Thanks for any input you might offer.

 

I'd bet the water never gets hot enough to kill off any bateria growth in the tank (over 130 degrees). Generally, foul odors in DHW is caused by bateria; probably holds true for what you're experiencing, unless it some sort of chemical breakdown...

 

Don't worry about it. I've seen that color as well as black & rust red/brown. The smell isn't unusual either. All of it is a result of the water becoming "neutral" as it will in any closed loop system. Remember, one of the worst things you can do to a closed loop system is to add fresh water.

 

Not sure just what you have there. But on old boilers the water can stink like H*** They just called it dead water . Dont know if thats what you have there

ED

 

Grady.......why is it bad to add the fresh water to a closed loop system?

 

For one. Every time you add water you add air.

 

Mattison is right. All water contains some dissolved oxygen. The oxygen & other dissolved elements or compounds are either deposit forming or aggressive. When you add fresh water you are adding "stuff" that isn't good for your system. In commercial systems, water treatment is a big deal & big business. Ideally, once a system is filled, not another drop of fresh water should be added.

 

Given all that....then do you think the cold water (make-up) supply valve was closed for a reason, and that I shouldn't have opened it?

Aside from that...should I be attempting to drain sediment from the water tank once a year? (Assuming that doing so would cause the tank to draw make-up water)

Thanks!

 

The make up water valve should be left closed. When doing so, I strongly urge the installation of a low water cut-off switch (you may have one already). A low water cut-off can save a boiler from "dry firing" if the water level in the boiler drops too low.

I presume the water tank to which you refer is the expansion tank. If so, I don't believe in draining them unless you have a problem. When you drain the tank, you not only introduce fresh water but also air. I much prefer the bladder type expansion tanks.

 

Hi Grady

Thanks for your input on this.

No, by water tank I meant the tank in the gas-fired water heater. I have always read that you should drain a bucket of water from the drain-valve at the bottom of a water heater at least once a year to help flush out and prevent sediment build-up.

But in a closed system, I assume this would necessitate replacing the water.

To answer your other point: I do not believe that a low-water cutout was installed---at least, there is nothing I can see attached to the system besides the traditional relief valves. If that is the case, then perhaps I should leave the water supply line OPEN... I can tell you this: The system seems to be operating better (more even distribution of heat) since I opened the supply valve.

By the way, I checked, and this particular water heater is rated for both potable water and space heating. Mine is dedicated to space heating.

Thanks again!

 

Here's a good tutorial on flushing tanks from this site:

http://forum.doityourself.com/showthread.php?t=134483

Better add this :For potable water heaters, not closed loop.

 

You say the system works better with the feed water on. You probably have a very small leak somewhere which you may or may not be able to find. There are hundreds of thousands boilers out there with the supply valves open & have been for years. Do what works best for you. What I said in previous posts is great in theory but we don't live in a theoretical world.