Weil Mclain ultra gas-fired water boiler 399

there is a large discrepancy in the outdoor temp.

If that controller is like the U-control in the Ultra 3 boilers, there is an adjustment accessible from the control panel where you can correct it. Mine is 2 or 3 degrees off, I forget which way. But the location of the ODR sensor and the outdoor thermometer is a little different. Both are in the shade at all times in the winter.



" For example, this morning the outdoor temp was 16 but the boiler says it is 27..."

"Could this outdoor temp discrepancy be causing the boiler to run more often"



I would think it is the opposite: that it thinks outside temperature is higher than it is, so it would make the boiler run at a lower temperature than need be. To maintain the required inside temperature, I would think your boiler would run longer, but less often.



" Previous reading were similar when is was 11 the boiler readout was 27 (supply 180 -target 182)"



Those temperatures seem awfully high for a condensing boiler. I would assume you get no condensing at all. Hence the high fuel consumption.



Was this system designed? Was there a room-by-room heat loss done? What is the nature of the emitters? Baseboard? What size? radiant? In slab? panels on walls or ceiling? etc. If you have enough emitters, you should be able to run lower temperatures. Are the reset curves set right?

"Was this system designed?"

"To determine the size boiler to replace the 1925 one, all radiators were

measured to determine the total radiation in square feet and that was

multiplied by the conversion factor for hot water (185) which resulted

in a BTUH load of 303,159."



For any given water temperature, that would give you the amount of heat that could be delivered to the load. But that would not tell you the amount of heat needed by your load to maintain the desired indoor temperature with a given outdoor temperature. You will still need a room by room calculation of the heat load, preferably at two different outdoor temperatures. One should be at the design day temperature and one could be quite a lot warmer, say 50 to 60F.



From that you can determine the supply water temperatures needed. And with that, you can calculate the required reset curve(s). I did all that and it worked, but for my system, the heat loss calculated exceeded the actual heat loss by enough that the reset curves I calculated were too high. So I reset one end or the other by trial and error until I got them right. I had a plan, though, it was not at random.



For my system here in New Jersey for a small Cape Cod type house, design temperature is 14F and I run between 76F and 120F in the radiant slab, and between 110F and 135F in the baseboard zone.



If you are running around 180F in your system you are almost certainly getting no condensation, which costs you a fair bit of efficiency. Also, the outdoor reset will save you even more efficiency than the condensing feature does because it matches the heat supply to the heat need. And except for outdoor temperatures at or below design temperature, if the system is asking for 180F supply temperatures, your resets are almost certainly wrong.

One other thing

This is not related to the outdoor sensor issue. I don't know about your area, but here in Virginia it has been colder than in many previous years for the months of November and December. This will obviously affect your comparisons to previous years.



Rob