Lochinvar - "System" Temperature

Lockoutvar

Currently have a Lochinvar KBN285 with priority DHW and 3 zones w/ circulators (single temp).

I have a questions about "system" temperature and the "system" temperature sensor.

For whatever reason, the system temperature always seems to lag about 10-15 degrees behind the outlet temp. The temp is often even a few degrees below the inlet temp. My hunch is that it is probably not placed or attached correctly. Because of the lag, the outlet temp ends up crawling up towards high limit and then eventually once the system temperature catches up, it ends up going past the SP + offset, in some cases.

The sensor appears to be below the 3 zones on the supply side. I have circled it in the pictures below (if I am correct).

I am not familiar with what the sensor should look like or how it should be attached, but does anything look off with it? I know the supply should not necessarily match the outlet temp, but I think it should be a lot closer and definitely now lower than the return / inlet temp. Perhaps everything is as it should be, but it just seems a bit odd to me that the system temperature on the supply side would be below the inlet temp.

hot_rod

I strap it to the pipe with a hose clamp, then insulate over . With a boiler piped primary secondary, the temperature at that point will be a “mixed” temperature. Perhaps when all zones are off conduction may cause some temperature rise?

Lockoutvar

Thanks. I understand it would be mixed, but it is often 15-20 degrees below the outlet and in some cases a few below the inlet. How can it be below the inlet temp (even after running for a while)? Does it look like the sensor isn't close enough to the pipe, perhaps? I have zero experience with this stuff so not sure what part of the wire is actually the sensor and or how close it should be. I have some "PTSD" from this thing breaking down and not working correctly so I am overanalyzing everything myself because I can't keep calling people over.

EBEBRATT-Ed

The return water passing through the manifold will dilute the supply temp from the boiler down so the actual supply temp from the boiler will be hotter than the "mixed" temp at your sensor location. I don't see the sensor in your picture but it needs to be strapped tightly to the pipe.

Its possible that the flow on the boiler pumps and through the boiler and the flow through your zones is not balanced properly which can cause issues.

Lockoutvar

Oh - I thought the sensor was the wires. The sensor is underneath that piece of foam insulation in between basement and 1st floor zones (directly to the right of my circle).

But the system temperature is currently reading 15 degrees below inlet and 25 degrees below outlet temps. I would think inlet should definitely be less than system… is that not correct?

hot_rod

You can confirm the sensor is accurate by holding it against a glass of ice water, and against a pan that had boiling water, for example, or strap another temperature sensor next to it, under the insulation.

Or with an Ohm meter and use the values in the manual. Page 30 maybe?

If none of the zone pumps are running the temperature in that header pipe will drop.

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