Maxim 255 Temperature difference

Woodman1

New Member
Jan 15, 2018
79
Michigan
I'm pretty sure the "mixing valve" is central boilers attempt at boiler protection. Basically their version of a danfoss valve. I have never seen one personally so I don't know how they are designed to be plumbed. To go back to the original post I thought the question was why the op was losing 20 degrees of heat from the boiler to the valve. I'm still guessing he's not and the water leaving the boiler is the same temp as it is hitting the valve. Too bad he can't get an accurate reading with the ir gun this could be solved in 2 minutes! Lol!!
 

Woodman1

New Member
Jan 15, 2018
79
Michigan
Thinking you're onto something here, I'm seeing lots of 3/4" elbows, 3/4" valves and fittings, do a pump head calculation on 130ft 1" pex (3/4" ID?) 8-90els, and 10gpm and you have a pump head pushing 30ft. Well outside the 007 pump curve.

Think I'd get rid of that mixing valve too but I don't know the purpose of it.

Correction: 1" pex is .875 id. better but still could be outside a 007 pump curve. Don't know the required flow rate however, if it's 5 gpm then the 007 would be fine.

Anyone trying to push more than 7-8 gpm through 1" pex is going to be fighting an uphill battle. 5 gpm with a 40 degree delta t delivers the same amount of btus as 10 gpm with a 20 degree delta t. Just make sure you have the boiler protection installed correctly
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
Stratification means different temperature from the top of the boiler jacket to the bottom. It could be possible that if your supply water is coming off the bottom of the boiler and your temp gauge is up higher, that could explain the difference you are seeing. Hotter water will seek the high spots.

If this is occurring depends on things like boiler design and flow through the boiler (causing temperature mixing) . Most boiler designs pull the hottest water off the top and return at the bottom. Less jacket volume and good flow through jacket will stratify less, more volume and less flow will stratify more- again boiler design plays a big role here.
O.K. I understand now. I'm not sure about the internals of the boiler (I will have to see if there is a diagram available to see where the water is being drawn from in the tank).
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
When you say "mixing valve" do you mean the one way check valve on the return side in the pump pictures?

I was talking about the thermostatic valve. What is its purpose in this application?

And is the 007 the only circulator in the whole system? You mentioned boiler is close to house, but you also mentioned 100' of pex.
It was something the installer insisted was necessary for the boiler installation. Basically it only opens the valve once it gets up to 160 degrees F. I guess the thinking is that it will send the water flow directly back to the boiler until it gets up to temperature. Once the valve is open it will send water through the heating loop and when it is closed it just returns it immediately back to the boiler. And yes the 007 is the only circulator pump for the one loop.
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
I'm pretty sure the "mixing valve" is central boilers attempt at boiler protection. Basically their version of a danfoss valve. I have never seen one personally so I don't know how they are designed to be plumbed. To go back to the original post I thought the question was why the op was losing 20 degrees of heat from the boiler to the valve. I'm still guessing he's not and the water leaving the boiler is the same temp as it is hitting the valve. Too bad he can't get an accurate reading with the ir gun this could be solved in 2 minutes! Lol!!
That thermostatic valve is designed to be closed when the water temp is under 160 degrees and open at higher temps. When it is closed it sends the water immediately back to the boiler (bypassing the heating loop). I think they want that installed to help the boiler get up to temperature quicker when the water temp drops below 160. The IR gun did give me a temp reading of 180+ on the flange of the pump (but it is all over the place when shooting the pex and elbows).
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
Thanks for the feedback everybody. I think I'm going to pick up the variable speed Taco 0015 (and maybe some in-line temp gauges) and see if that makes a difference on the temperatures. I'll post the results of the new pump so everybody is aware of the outcome.
 

Eureka

Member
Feb 4, 2018
246
NW Wisconsin
Thanks for the feedback everybody. I think I'm going to pick up the variable speed Taco 0015 (and maybe some in-line temp gauges) and see if that makes a difference on the temperatures. I'll post the results of the new pump so everybody is aware of the outcome.
https://www.supplyhouse.com/SharkBite-24441-SharkBite-Temperature-Gauge-with-1-Tee-Lead-Free
These are a handy all in one solution for temperature readings. You can also do a tee and stick a temp gauge in that just make sure the well sees actual flow. If it’s just stubbed into the tee it won’t be accurate. Supply House is great for this stuff. I used Watts gauges into tees and also have a couple Sharkbite gauges. The latter are real handy just cut and push on.
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
So I installed the Taco 0015 pump this morning....no difference at all (all three settings). The temp at the thermostatic valve is still 170-175 when the boiler control unit is reading 185-190. I've ordered a pipe clamp temperature gauge and a long temperature probe and should be getting those on Tuesday. I'm going to take some readings at various spots along the pex (including right at the supply side on the boiler) and the temp of the water again in the boiler (I think the cord will be long enough to get it right to the bottom). Stumped.....
 

maple1

Minister of Fire
Sep 15, 2011
10,008
Nova Scotia
I'm pretty sure the "mixing valve" is central boilers attempt at boiler protection. Basically their version of a danfoss valve. I have never seen one personally so I don't know how they are designed to be plumbed. To go back to the original post I thought the question was why the op was losing 20 degrees of heat from the boiler to the valve. I'm still guessing he's not and the water leaving the boiler is the same temp as it is hitting the valve. Too bad he can't get an accurate reading with the ir gun this could be solved in 2 minutes! Lol!!
I'm not quite seeing the need for a mixing valve at all in this pellet boiler application. If the boiler can supply say 180 degree water and flows are correct, it shouldn't see close to 140 in the return with all good insulated piping everywhere and a typical 20dT thru what I think is only one heat exchanger? Plus there is also the factor that with a pellet boiler there should be little risk of creosote condensation since it should burn clean to start with.

But I have no pellet experience....
 

Woodman1

New Member
Jan 15, 2018
79
Michigan
I agree. However, I don't know anything about pellet boilers but in my head they should be able to maintain a constant temperature similar to a conventional fossil fuel boiler. I still think op will find out water temp leaving the boiler is the same temp that the gauge at the valve is reading
 

maple1

Minister of Fire
Sep 15, 2011
10,008
Nova Scotia
I'm kind of curious about the boiler innards. Having the outlet at the bottom like that usually isn't the best (at all) for supplying the hottest water, but if there is a stand pipe kind of thing going on inside then he should be getting the hottest water. But with just the one circ for the whole entire business, there must be some stratification going on inside it. Maybe they put the outlet on the bottom with a pipe to the top inside to try to ensure that the circ got mounted down low so there would be more head pressure to it.
 

Cliff DeCarlo

New Member
Mar 12, 2019
18
Easton, NY
I'm thinking now that there may have been some air in the loop? I've installed the Taco 0015 and have left it on high all week. Today the temps on the gauges at the thermostatic valve got up to 182. Maybe the higher pressure pump has pushed some of the air out? I've taken several temperature readings (with a pipe clamp sensor and a thermistor taped onto the copper/brass fittings). I also took the temp of the water in the boiler tank to see if it matched the reading on the boiler control unit (it did within 1.5 degrees). The temps on the pipe clamp/thermistor were all about 30 degrees less than the boiler (readings about 160 at the pump and at the thermostatic valve, whose gauge was reading 182). The temps (taken using the pipe clamp sensor on the copper supply side of the heat exchanger) also read 162 at the supply side and 140 on the return side (the furnace blower was running when I took these temps). Definitely better, I wonder if I leave the pump running on high for a little bit longer if more air might work itself out of the lines.

As far as the internals of the boiler go, I looked in my owners manual and also did some googling to see if I could find a schematic...I could not. So I really have no idea where the actual supply/return sides are coming from on the tank. I assume they designed it like a normal hot water tank and are drawing the supply from the top and the return to the bottom...but I honestly have no idea.