Troubles with non-condensing boiler

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Old 10-25-13, 09:12 AM
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Troubles with non-condensing boiler

Hello All,

I am total novice in this space but just went through second non-condensing boiler in 18 years due to rusted heat exchanger. Had two different professional plumbers installing and modifying hydronic heating system in my house and they both have different opinion on what caused the boiler damage. I have Super Hot MG series non-condensing boiler installed 6 years ago and this week it start leaking. The system is built as follows:
- boiler loop with pomp supplies water-glycol mix at temperature between 160 - 185 F to a mixing circuit and to DHW tank via valve controlled by DHW sensor
- mixing is provided by Danfoss 1" TMV
- system loop with separate pomp feeds three loops with thermostat controlled valves
- there is Tyco controller installed to provide priority heat control for DHW tank

Have few questions:
1. Does boiler loop need to run always (temperature of mix has to stay above 140F)?. In summer when hydronic heating heating is off this would mean a lot of lost energy (the only demand for heat coming from DHW).
2. Boiler can bring temperature from ambient to 140 F (cold start) within 17 secs, is it enough to create condensation which can destroy the heat exchange element?

Thank you for your help.

Jackplumber
 
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Old 10-25-13, 09:45 AM
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Hi..

Are you testing the glycol yearly? It can turn acidic if not maintained...

What type of heat emitters? Is this an in floor radiant with a mixing valve?

Wee would need to see a drawing on how its piped with the loops primary and secondary piping to make a call if its correct..

Boiler loop needs proper return temps above 140f I believe but a 17 sec fire time to 140f sounds troublesome..


What size is this boiler? How many square ft home?

Let us know and take some pics....

http://alliedboilers.com/wp-content/...ice_Manual.pdf
 
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Old 10-25-13, 10:47 AM
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from ambient to 140 F (cold start) within 17 secs
I somehow don't think that's even physically possible!
 
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Old 10-26-13, 05:22 PM
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Few answers.

17 secs was my typo, it is more like 77 secs.

Glycol is checked on annual basis, last time in April of this year.

The Super Hot furnace delivers 125 k BTU/h (per specs).

Here is the drawing:

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Jackplumber
 
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Old 10-26-13, 06:41 PM
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Even 77 seconds sounds like an awfully short time to bring water from ambient to 140...

Jack, are you sure that it's actually a 'loop' on the right side there? I can't see as how you would get much flow into the zones with that setup.
 
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Old 10-27-13, 03:40 PM
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Hi NJ Trooper,

I have missed a balancing valve in the secondary circuit. It is located between output and input to/from zones.


Jackplumber
 
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Old 10-27-13, 03:56 PM
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Not sure where you mean Jack...

Can you draw it in and repost the picture?

Something about that system diagram is not 'normal'.
 
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Old 10-27-13, 05:41 PM
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Updated diagram.

Name:  Home_Hydronic_System_131027.jpg
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Tyco - ZVC 405

Jackplumber
 
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Old 10-28-13, 06:05 PM
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To answer your questions:

1. Does boiler loop need to run always (temperature of mix has to stay above 140F)?. In summer when hydronic heating heating is off this would mean a lot of lost energy (the only demand for heat coming from DHW).
No, it does not.

2. Boiler can bring temperature from ambient to 140 F (cold start) within 17 secs, is it enough to create condensation which can destroy the heat exchange element?
Even 77 seconds seems like a very short time to bring the water that hot from ambient...

Condensation does not come from rapid temperature rise. It comes from a lot of cool water returning to the boiler for prolonged periods of time.

Once the water heats up the condensation dries, and the acid becomes inert.

For acid to cause damage, there must be water.

The faster the boiler (and the return water) heats up, the sooner the condensation that has formed dries out, and all is then OK.

It's BETTER for the boiler to heat up faster... though I still question the 77 seconds.

Jack, can you post some pictures of your installation showing all the elements that are in your graphic drawing please?
 
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Old 10-29-13, 08:34 AM
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Here are two pictures. I can post more, if required.

Thank you for explaining condensation phenomenon. Based on your comments I believe the main reason of my problems is poor protection if boiler (return water temperature control). Wondering what solution should be implemented in my case.

Jackplumber

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Old 10-29-13, 09:30 AM
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Jack, those pics help a lot...

What type of heat emitters are in your home? It appears that you may have radiant in-floor tubing based on the fact that there is the TMV in the circuit?

What temperature is that TMV set at ?
 
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Old 10-29-13, 08:31 PM
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I have three separate radiant circuits and there are:
- three loops in the basement (slab heating) sharing the same manifold
- one loop in garage (slab heating)
- two loops between joist to heat ceramic tile floor on the first floor - sharing the same manifold

Temperature is set for 125F but suspect this may not be correct. Do not handy thermometer to measure.
 
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Old 10-29-13, 08:39 PM
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Jack you have a temp gauge at the zones... Whats it read after the boiler has been firing? Jack whats the TMV set at? You never gave an answer???

Also how does it corospond to the temp gauge at the boiler?

Can you take many more pics??? Boiler? And all angles all around?

Are you sure it was rusted heat exchanger from outside? Maybe it was water quality from inside??? Like PH issues or softener???

Who made this determination?

Its all hear say so far IMO....

18 yrs is a good run for a mod con IMO...
 
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Old 10-30-13, 11:45 AM
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Mike, this is a NON-condensing conventional boiler.

Jack, it would seem that the problem here is the fact that you are returning the cool return water from the floors back to the boiler with no form of boiler protection.

I am ... uhhhh... let's say... very unenthusiastic about the piping layout of your system. This setup wouldn't even be correct if you actually HAD a condensing boiler on line.
 
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Old 10-31-13, 08:30 AM
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Hi Lawrosa,

Here are more pictures. Please advise which areas of this installation you may have special interest in.

Thank you for following up.

Jackplumber

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