Boiler Running Full Tilt, Cold House
This Lochinvar has been running at 100% modulation for days after heating without any problem for years. It has not been de-rated in the programming; CO2 is 8.5%, flue temperature is 71F. Technical support at Lochinvar thinks that the HX is occluded, but I think we would see a higher stack temperature. I have my own theory. What do you think?
Two btu per sq ft for degree difference for a slab
Comments
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it isn't pushing enough air through the gas valve one way or another. air leak, blower running slow or damaged or clogged, something else clogged or iced. if it were a gas supply issue the mixture would be off. it is burning right just not enough volume. hx filled mostly with condensate?
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has it been taking on fill water that could have scaled it up?
What type of heat emitters?
Is it primary secondary or a LLH? The display shows pump 1 and 3 activated?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
The fan sounded max'd out and the condensate was dripping steadily. When I go back, I'll clock the meter.
It's an Eichler, i.e. radiant. One thermostat, one pump, piped directly into the slab.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab1 -
Combustion is good must be underfired. I would think the flue temp would be higher if the HX was the issue.
Doesn't the flue temp follow the water outlet temp?
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not if it is the combustion side of the hx restricting the airflow. remember the gas valve is essentially a carburetor that meters the fuel based on airflow.
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Shut the water feed off to the boiler. I'm suspecting a leak in the underground. Those Btu's are going somewhere or the software is lying to you. If the pressure drops and boiler shuts down on a water pressure fault or low water cutoff shuts down the boiler then you will know
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it doesn't have any way to actually measure the air or gas flowing through the boiler, it just either know what voltage it sent to the fan motor or maybe has a tachometer lead on the fan motor and calculates the firing rate from that.
@EBEBRATT-Ed the flue temp is a function of the return water temp. the hx is arranged so the flue gases hit the return water last so it can approach the return water temp
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If the boiler is firing at 100% then its adding all the Btu that it can produce to the heating medium. All those BTU's are going somewhere. No matter how bad your combustion is. If he is leaking water he is just heating feed water that is just draining.
And I don't think he has a dirty he exchanger as it still in the condensing mode.
@mattmia2 I doubt the software is lying, that was saying sarcastically. The hall sensor in the ECM motor communicates with the CPU to tell how fast the ECM is running. the speed of the ECM motor dictates the BTUS delivered into the system. If the motor is calling for 100% RPM then its asking for the maximum BTU input.
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Have you verified actual fluid and flue temps? Have you placed it in service mode and manually adjusted the fan speed to verify it's hitting both ends (high fire is usually around 8900 RPM)? Have you turned off the feeder to verify it's not just pouring everything right back out under the slab?
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I chatted with the folks at the Sermeta booth at AHR this week. As @pedmec mentioned the fan speed regulates the firing rate of the burner.
My specific question was if the burner could run at it's lowest firing rate for long periods without any issues. As that question came up here recently. Yes, as long as the gas valve is adjusted to the fan speed. The correct valve/fan assembly, and adjusted accurately. Combustion trimming is be a must.
He did mention the burners for the USA market tend to be the version that looks like a mesh or steel wool wrap. The burners in Europe are laser slotted stainless tubes. This has to do with NG gas quality and blends in Europe.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Take a look at the picture and you will see the water feed turned off. That was the first thing I did and the water pressure stuck at 15psi for as long as I was there.
@GroundUp The fluid temperature shown on the screen is fairly accurate by feeling the pipes. The stack temperature was verified by my combustion analyzer. I did not verify the fan speed, but I heard it ramp up after ignition and it seemed to follow the displayed percentages.
It's been raining heavily here and I thought a high water table might be sucking heat out of the slab, but I still have other things to test before settling on that. I'll go back soon and clock the gas meter. Maybe pull the lid off the HX to see if anything looks amiss.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab
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That only tells you how fast the fan is turning, not how much air it is moving or how much air is moving through the gas valve. In my UFT the fan pushes through the gas valve so if there is a leak between the fan and the gas valve it won't get the flow it claims. About half of the potential problems here are engine manifold vacuum leak 101.
Could you get enough flow through a bad diaphragm in a pressure switch to significantly affect the firing rate but still close the switch?
Could the inlet be restricted enough to reduce the airflow significantly but still make the pressure switch happy? What happens if you disconnect the inlet piping?
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I had a customer with a similar condition. Early munchkin serving a completely uninsulated slab section on S.F. hillside. Pre thermal camera. After much theorizing and measurement I found the smoking gun. Being on a hill there was little question about what way heated water would flow if that was the loss case. After six small holes were drilled in the joint of the driveway below the structure the heat flow was identified. It would have been easier with a thermal camera. Running flat out for 24 hrs will have a loss signature somewhere. The volume of dripping condensate is proof positive of BTU development.
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If it has been running at 100% for several days their gas bill will tell you if it has been heating the groundwater or if t is undefiring.
if it turns out that it is really firing at 100% it is very likely the storm sewer or drain tile has clogged.
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