Hot water turns cool.


  #1  
Old 09-28-06, 09:16 AM
J
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Hot water turns cool.

I have a Trianco boiler with tankless coil and no storage tank. Problem is hot water starts out hot and after a few minutes cools off, not bad in the summer but much worse in the winter. Affects all faucets: shower, sinks, etc. During a shower the burner kicks on when more hot water is called for but runs its cycle & then shuts off (after the boiler water comes back to temp.) for a few minutes, however the water in the shower cools off considerably. The mixing valve was replaced a couple years ago but I"m thinking along the lines of the tankless coil? It's almost 20 years old (original) & we do sometimes have some problems with some fine sediment from the town water supply. The heat always seems fine in the winter when that's on. Is there anything else beside the coil losing it's heat exchanging capabilities that might cause this before going through this expense?

Also is there any way to avoid the sometimes drastic drop in hot water temp when the heat kicks on in the winter. I realize it's from the cool/cold water from the baseboard piping going back through the boiler but is quite unpleasant during shower.

Thanks,
Jon
 
  #2  
Old 09-28-06, 03:14 PM
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Lack of hot water

You can replace the coil but you would be WAY ahead of the game to install an indirect water heater. They are not cheap but far superior to a tankless coil.
 
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Old 09-29-06, 04:36 PM
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I never really knew of the indirect water heater before now but after reading about them they sound good. After reading some other posts on here my main question is if anyone knows if my boiler is a good canidate for this, good for cold starts, if it's a large capacity boiler, etc. From the little I know of it Trianco doesn't make this model anymore (dbc-115), they don't seem at all common, but are they good boilers?
Thanks again, there is some great info on this site!

Jon
 
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Old 09-29-06, 05:40 PM
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Trianco

I've only worked on a few Trianco Boilers but from what I recall of those, they held a relatively large quantity of water. If this is the case, an indirect is probably not practical because of the "long" heat-up time needed for the large water volume.

Here is a quick "rule of thumb" test you can do: Turn off the power to the boiler & allow it to cool completely (will likely take several hours). Without having the thermostat calling for heat, turn the switch back on & measure the amout of time it takes to heat the boiler to aprox. 150. If it takes under 2-3 minutes it most likely would be a good candidate for an indirect.
 
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Old 10-04-06, 12:29 PM
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Unhappy Test results

OK I did the boiler heat-up time test and the results are the following (I let boiler cool down to about 100 degrees):

from 100 to 150 it took about 5 minutes.

from 100 to ~195 about 10 minutes (this is when the boiler turns off), I think it usually runs between ~175 to ~195 degrees.

So I assume not really good canidate for indirect, however, do these temps seem correct being this high or should they be lower?

Also maybe I should've added to the original post that after about 5 or 10 minutes of the water cooling off that it does have a 'second wind' of hot water which lasts for about another 5 minutes or so & then goes through the cooling cycle again. Does that change anything to what my problem could be? Could it still be the tankless heating coil even though it heats back up again?
 
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Old 10-04-06, 05:09 PM
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Tankless coil

What you are experiencing is typical tankless coil. You could run an indirect at 140-150 & add a tempering valve. This should give you the desired effect at the tap while giving the boiler a chance to come up to temperature. What is the btu output of the boiler?
 
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Old 10-04-06, 05:32 PM
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Gross output 115M
Net output 100M

That's what's stamped on the boiler, if you were asking anything other than that I'm not sure.

It's a Trianco DBC-115
 
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Old 10-04-06, 05:43 PM
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Output

With that output, it should handle an indirect easily if put on a priority zone with it's own dedicated circulator.
 
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Old 10-04-06, 05:55 PM
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So the 5 minutes it took to go from 100 to 150 is ok? Also should the boiler be kept to kick on at a certain 'low' temperature to avoid going down to say 70 degrees?
 
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Old 10-04-06, 06:01 PM
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Maintaining temperature

It probably wouldn't cost much in fuel to maintain 100-110. I do suggest you talk to a supplier of indirects about your boiler heat up time. I think you would be fine, but that's me & I'm just one person.
 
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Old 10-15-06, 05:12 PM
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Thumbs down Changed coil to no avail

Put new coil in (had nothing better to do on a Sunday,,NOT), but didn't help situation, actually I'd say it's a little worse. Now water was hot at very beginning of shower but then went to warm & stayed there, no fluctuation like before. And no I didn't change any settings that would cause this as far as I know. Didn't change settings in control box, still 180-200 with 10 diff & mixing valve still set at max hot.

Questions about my setup though are:

I basically drained the hot water system via the mixing valve, could taking this out & putting it back in have an adverse effect causing part of my problem? (changing mixing valve would be nice easy job after changing coil!)

Second, the hot water portion of the piping has a half inch valve to isolate it from the rest of the house piping (normal I'd say), but just after the valve & before the 'T' for hot water coil or cold for mixing, it goes through a 3gpm reducer. Is this where the reducer should be or would it work better after the 'T' on the mixing side to avoid too much cold water to be mixed or would this cause the water going through the coil to not heat up enough?

Third, when I closed the above mentioned isolation valve it wasn't closing all the way, is there a chance it's not opening all the way too causing me to have less water then I should & is there any chance that 3gpm reducer isn't doing it's designed job & could be partly clogged or need to be moved or re-moved?


By the way, the only reason I went with just replacing the coil was that it was the easiest/cheapest thing for me to do myself without getting a crazy bill to have some other work done. One local oil co. I talked to just wants to tear out entire system & put new boiler in... for $5000! Instead of even looking at my existing situation. I have no problem putting some money out for a system if I end up needing it but wasn't really happy with that reaction.
 
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Old 10-15-06, 05:18 PM
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Piping configuration

Sorry, you lost me with your description of the piping. The flow restrictor could be the problem as well as the mixing valve. Not sure of the location of the isolation valve you spoke of. Some pix would be a help.
 
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Old 10-17-06, 05:20 PM
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Talking Got It!

After changing the coil (with not much good luck), I changed the mixing valve, isolation valve (stop valve, which when closed shuts off the water to the coil & hot water system, which was leaking & seating incorrectly) & removed the 3gpm reducing valve. I kind of think it was the reducing valve that may have been fouled & was worried that taking it out would cause the water to go through the coil too fast & not come up to temp., not the case at all! Not sure if the system was designed with that reducer or was put in later by someone in effort to fix hot water problem in the past. I might be making the boiler work a little more by heating more water but I'm happy with the results.

As I said in earlier post, I always had to have mixing valve maxed out for hot (even after it was replaced a few years ago), now it's in about the middle & still plenty hot. Had the hottest, most consistant showers last night & tonight since I moved to this house 5 years ago! As long as this lasts a few years I'll have to say my $300 investment was a good choice compared to the $5000 the oil co. wanted to charge me to 'fix' the problem.

Thanks for your input Grady, hopefully as with many of these posts this one will help others in the future.
 
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Old 10-17-06, 05:54 PM
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Thumbs up Re: Got It

Jon,
Thank you for posting what you did to cure your problem & as you said, hopefully someone else can benefit from your experience. That's a large part of what we are all about here. Thanks again.
 
 

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