Buderus Indirect Hot water tank too hot

[kdt]

I recently had a Buderus G115 boiler installed, with a Buderus ST-150 40 gallon indirect hot water tank. The aquastat for the hot water tank is a Goldline SP-30D, one of the controls recommended by Buderus. The zone valve is a Taco 1 inch. The goal was to get 120 degree DHW. The DHW was running hot compared to the upper limit set on the aquastat, so we lowered the high temp to 105 degrees, with a 5 degree differential. (With this setting, the stat would call for heat to come to the tank at 100 degrees, and SHOULD stop calling at 105 degrees.) With this setting, the temp goes as high as 140 degrees and never lower than 120 degrees. Many times it is 130 degrees (all temps measured at the tap in the kitchen).
Can anyone explain why this is happening? The aquastat appears to be wired correctly and all the jumpers are set correctly. It was installed by a pro, and he is somewhat stumped by this. Perhaps the sensor is bad, but it is pretty close, because when the temp in the tank is 130, the stat won't go on until you turn the dial past 130. Is the Taco zone valve not closing, thus allowing hot water to continue to circulate in the zone? Any insight would be greatly appreciated!

[dave72370]

KDT,

Do you not have a tempering valve on the output of the DHW? I have a Buderus G115 with the ST-150 as well. The difference is that I run the Tank at 140 degrees to avoid as issue with bacteria and disease. The comment below was pulled form the america health journal:



There is also concern for increased risk of bacteria growth in water storage systems with such tepid water temperatures below 120 degrees ((ASTM F-444.88). Patrick J. Higgins, a master plumber and plumbing consultant in Frederick, Maryland, cautions that water heaters set below 120°F pose a health risk by inviting the growth of bacteria, including the one that causes Legionnaire's disease

the way around this is to set the temp to 140 and use a tempering valse to bring it down to 104 for most faucets.

Sorry I could not help ith the aquastat issue, I use the buderus logamatic controller to control my DHW tank, but I thought that you might find the article interesting on a low temp seeting in the tank.

Dave

[oil lp man]

When another heating zone (probably the longest zone)is calling and the indirect water heater isn't calling, put your hands on the indirect zone piping and see if its heating up. If it is either the indirect storage tanks' zone valve is slightly stuck open or it is being lifted open by the circulator.
Then you either need the zone valve replaced or piped differently.
All circulators are better but more expensive.

It would probably save a lot of time if he just installed a seperate circulator for the indirect piped close to the boiler. This is the correct way to do it. The supply and return pipng should be the first zones off the headers.
The circulator should be low near the storage tank. And a check valve to prevent overheating.

[Edited by oil lp man on 01-14-2005 at 12:00 AM]

[nutshell]

That tank is not designed to put out 120 or so degrees. It should run at 150 degrees, a mixing valve should be installed to temper it to what your needs are, like 120. You get a much more even temprature and your hot water will last much longer. You should also have flow checks on all zones to keep heating water from migrating when there is no call for hot water. When I install these I like to use a Taco zone control to make the system run priority hot water

[Edited by nutshell on 01-14-2005 at 06:51 PM]

[beenthere]

Also check for proper wiring of the zone valves, i've seen them missed wired that a valve would open when another zone was calling.

[kdt]

Thanks for the feedback and tips. It appears pretty certain that the zone valve is malfunctioning, letting hot boiler water into the tank when it is not called for.

Dave, I like the idea of a tempering valve and I plan to up the temp for health reasons. There seem to be several tempering valves out there on the market. Which one did you use?

[r&mcc]

Are you sure it was installed by a pro? A pro would've installed a tempering valve and would've probably used a seperate circ. pump instead of a zone valve.

Conbraco makes a decent tempering valve. Never had any complaints.

[dave72370]

I just used a regular Watts tempering valve

[kdt]

r&mcc

He will be installing a separate circulator and a tempering valve next week, at no extra charge. I am pleased that he is willing to make it right. He provided a lot of little "extras" at no charge, such as separating my first and second floor into separate zones. Perhaps it should have been better up front, but one sign of a "pro" is the willingness to make the job right if mistakes were made.

[r&mcc]

I'm surprised it wasn't done this way to begin with. I am pleased to hear that he is doing it at no charge. It sounds like he got caught trying to cut corners. Most customers probably wouldn't have been as perceptive as you. your contractor is doing the right thing by fixing his boo boo for 0$. Let us know how the system works after mods have been done.

[Panama]

A TACO 1" zone valve is too slow and too restrictive for DHW use. A White Rodgers 1361-103 is a much better choice IMHO.

[kdt]

Update: They installed a Honeywell tempering valve off my Buderus hot water tank, as well as the separate circulator to supply the tank. The valve seems to work OK, but there is a complication. When the valve is set at 120 degrees (the max it can go), the water at the tap is 140 degrees for a while, then it drops down to 120. Looking at it further, I noticed that the cold water side of the valve gets very hot once the hot water is turned off. The hot water is migrating through the tempering valve and over into the cold water supply line. In a short time, the cold water supply line to the tank is very hot and the main supply to the whole system starts to warm up. Once the hot water is turned on, the cold ends up taking over and the mixing works OK. My concern is the wasting of hot water as it heats up the cold water pipe, not to mention the HOT initial water at 140 when it first comes on. I then pulled out the manual for the Honeywell tempering valve that was left after the install. There it clearly shows that a flow check valve should have been installed on the cold side. One was not installed on mine. I'm just curious: Is it a standard item to have a flow check valve installed with a tempering valve?

[oil lp man]

You should have a domestic water expansion tank on the cold side, like an Amtrol ST5. Most cities have a check valve at your water meter already. But if not they may require it at the storage tank. If you have a well then its up to you if you want it or not.
But if it gets installed with no expansion tank the temperature and pressure relief valve on the storage tank will spit.

[dave72370]

KDT,

Where are you from? Just curious because I am in Mass and I see very few dealers pushing Buderus equipment, shame too. THey have very nice boilers and DHW tanks

Dave

[beenthere]

KDT, is your mixing valve directly above your indirect water heater.

If you can find the install instructions for your mixing valve, it will probaly tell you that it has to be piped up with a termal trap. If it isn't piped that way, that is why you get the 140 degree water at first.



[Edited by beenthere on 02-02-2005 at 07:23 PM]

[kdt]

Dave, I'm from PA.

Beenthere and Oil LPMan: Thanks for the tips. The Honeywell AM-1 Series mixing valve is right above the tank (a little off to one side). I have well water with a water softener just after the pressure tank when the water first comes into the house. The valve manual says that that an expansion tank is mandatory if there is some type of "V" device is used. They define a "V" device as "any device which turns the domestic water system into a closed system such as: backflow preventers check valves or pressure reducing valves." From the diagram it looks like this "V" device would be installed at the source of the water before it splits up into hot and cold lines. I don't appear to have any such device installed in my cold water feed line, unless the water softener can somehow be considered a "V" device. The cold water diverts to many other sources before it comes to the cold water feed to the boiler and water tank. This being the case,

1) could a check valve be installed right on the cold water feed to the mixing valve, without having to worry about the expansion tank?

2) Regarding the Thermal trap, it does show that on the piping diagram, but I'm not quite sure what it means. It shows a 6" distance from the cold water feed to the top of the tank, with the feed being 6" lower. Is that what they mean by a thermal trap?

The mixing valve is installed about 2 feet above the tank, and all the piping is well above the tank. When the cold water stops flowing to the valve when the hot water is turned off, you can feel the cold water line get hot very quickly, starting right at the mixing valve and working its way down the cold water feed to the tank. It is like there is this hot water loop, leaving the tank, then going back into the tank. It stays hot all the time, unless the hot water is used, then it gets cold only during that time.
Question: Is this something to be concerned about? My guess is that I'm cooling off the hot water tank by having this circulation, which will lower the eff. of the tank, thus making a very expensive tank less efficient, defeating the purpose of the tank. I'd really appreciate any comments.

[beenthere]

If you install a check, you will definitely need an expansion tank.

The cold water line getting hot, is a good example why you need the thermal trap, talk to your plumber about installing it.