Remove tankless HW from boiler?

[salty]

There is a boiler in one wing of a home I own that has a tankless water heater. This wing of the house is closed off and not occupied. I only run the boiler enough to keep pipes from freezing in winter. I would like to disconnect the domestic hot water since it sometimes makes the boiler run even though there is no use for domestic HW in that part of the house. Can I simply cap off the cold water supply to the exchanger, drain it, and forget about it, or do I need to remove the coil?

[RBM]

You could do any or all of the above, but it won't stop the boiler from running. The easiest thing to do is shut the power to the boiler when the heating season is over. The other thing you can do is turn down the aquastat that controls the domestic hot water. This is sometimes a separate device piped into the boiler's water jacket, and on newer boilers it's often a triple aquastat relay, which will have a low temperature cut in and a high temperature cutout within one box. In either case, just turn down the cut in control as far as it will go, and the boiler shouldn't fire unless a thermostat calls for heat

[salty]

Thanks. Are you saying that turning that control down all the way won't affect the boiler functions of heating of the house? That almost seems too easy. I thought that control would affect the water temp to the baseboard heating circuit as well.

I do shut down the boiler as soon as danger of a hard freeze is over. All the upper floor's domestic water plumbing and baseboards are empty, so I only need to heat the basement slightly to avoid damage to the foundation. I'm just trying to save as much oil out there as possible, and don't want to use any oil for heating domestic hot water that nobody needs.

[RBM]

Without knowing the controls you have on the boiler, I can't say for certain, but a typical modern boiler equipped with domestic coil, will have a triple aquastat relay, and the low temperature cut in is only to maintain tank temperature for the coil. The heating thermostat(s) will shunt the "T T" terminals in the relay and fire the boiler overriding the low temp cut in, and stay fired until the boiler reaches the high limit, or the zone calling for heat is satisfied

[salty]

Thanks very much. The boiler is only a year old, so I imagine the controls are what you are describing. To be safe, I'll try changing the settings, and wait around to make sure everyting is okay before walking away from it.

[RBM]

All you have to do is turn the low temp cut in all the way down, then turn a heating thermostat up and the boiler should fire, unless the tank temperature is already at the limit, in which case it'll fire after some hot water circulates, dropping it's temperature

[hallerb]

so you have a one year old boiler heating just barely to keep above freezing a unused space??

i would ask a heating contractor for the option of using the primary boiler to heat the unused space, thru a zone control.

this woulds shut down the second boiler entirely and may well cost less.

it could be plumbed by changing some valves to put the secondary boiler back on line someday.

plus theres no maintence on a unused boiler