Boiler Tuning for Hot water coil.....

I would suspect a mineralized coil. you can start out with exceedingly hot water(160/180) the mixing valve will temper it to the your setting on the mixing valve but then the water going through the coil is cold and can't absorb the heat fast enough The mixing valve can only mix if its getting hotter water imputed then its set for When the boiler cools down to the lower setting the boiler fires and runs to the hightemp limit at this point the cold water going thru the coil can absorb more of the heat it is exposed to. I would look into boiling the coil out with acid, or replacing the entire coil.

I think you'll find with tankless coil setups you need the hotter boiler water to keep up with demand at times. An indirect setup gives you a buffer so you can be a little lower in temp. Put your boiler temp back up to 180-160 deg. Consider an outdoor reset control and a hot water priority control set up. At the least, if your boiler is a higher mass, try an intellidyne or beckett heat manger. They allow the boiler to fire to 180 deg but will let it float down to 140 depending on the demand.

Unless your hot water temp has fallen off over time acid cleaning probably won't help.

Mike

benchmaker said:

thanks mike, i will look into a beckett, what do you mean by mass? and as i understand, the diff dial sets a drift too correct? i have mine at 15 but it was at 10, does this actually work against me when i raise it?

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The becket model is a "budget" type version of the Intellidyne heat manager that is actually made for becket by them. Basically it "learns " your heat demand with sensors and will hold off or activate the burner depending on the rate of change of the demand. Typically it will go into the "economizing" mode and hold off firing the burner if there seems to be enough residual heat in the boiler to satisfy the demand thereby minimizing burner cycles thus saving money. That's the idea anyway. It will start the burner at about 140 deg decreasing. The burner needs to have a shut off point of 180 plus deg rising. I use an Intellidyne with a cold start with indirect water heater using one sensor. A tankless coil setup would use an additional sensor. I understand the heat manger is most effective with a boiler with higher mass, i.e., more gallons the better, and low mass heat loads such as as baseboard radiators.

Mike