Millivolt Boiler Controls

bk14x32

Question: Are Millivolt Residential Gas Boiler Controls practical and reliable. 

Given: A standing pilot burner is required or Millivolt transformer.

Components: It appears that the basic control components are readily available. The Powerpile Generator, Gas Controller, Aquastat and Thermostat for small residential applications are available. Not sure if Low Boiler Water Cutoff or Weather Responsive Boiler Controls ave out there for Millivolt systems. Perhaps a switching relay could allow a 24 volt Low Water Cutoff to interrupt the Millivolt power circuit. Don't want to loose the generator to a transformer requiring outside power.

Reliability: Is the Powerpile Generator the weakest link in this control system? To insure reliability, should the generator be changed say once a year? Anyone out there with experience with Millivolt Controls please make positive or negative comments about their general use.

Thank you,

bk14x32

bk14x32

Clarification of the topic Millivolt Boiler Controls

The purpose of my question is to determine if Millivolt Boiler Controls are practical and reliable. If a Boiler Low Water Cutoff control is not available in Millivolt, rather than adapt a line or low voltage unit, my question is answered as to practicability. I want the boiler to have all the required and desired controls without being dependent on outside power. That is operating only on the 750 Millivoltage supplied by the pilot generator.

The Weather Responsive Boiler Control will be a topic of a future question. I am concerned about returning cool water to the boiler during the spring and fall. Could Boiler Thermal Shock, Condensation and the boiler running too long be caused by these controls? Could such controls require a bypass?

Thank you,

bk14x32

Tim McElwain

Millivolt Boilers are no longer offered

by manufacturers as a millivolt package.



The controls are however still available if you wanted to do a retrofit. The only problem is you would violate the code requirement for dual seated valves. Millivolt valves are all single seated.



The 750 millivolt pilot generators are usually good for up to 8 to 10 years. Mine on my furnace is looking at its 15th year. These were great systems with the option in a power failure to put the relay switch on manual and open either zone valves on manual or the flow check valve (circulators) and have gravity heat. The generators only job is to operate the gas valve through the safety controls circuit, it does not have sufficient power to operate anything else. With a boiler or furnace you will still have to have power to operate the circulator or fan on the furnace they are 120 VAC controls.



The LWCO can be wired into the system to shut of the gas valve in the event of low water. It is also possible to use outdoor reset as long as you have a relay control with isolated contacts to bring in the boiler.



As for low water return to a conventional boiler this can be avoided by using a system or boiler bypass to regulate return water temperatures to prevent thermal shock or condensing concerns.

bk14x32

Millivolt Boilers are no longer offered (reply)

Thank you for the detailed response to my post "Millivolt Boiler Controls".

I was not aware of the double seated valve requirement (for safety?).

I was asking if Millivolt Controls are practical and reliable because I have been researching the design of a Gravity Hot Water System (w/out circulator) and wanted controls that were independent of outside power. Your response indicates that the pilot generator is reliable but the current gas controller (gas valve) is not meeting present requirements.

Thank you,

bk14x32

Bobby K

Zzmac

Low water cut off for milivolt system

Are there any low water cut off switches that work on mili volt systems?

Zzmac

Low water cut off for milivolt system

Are there any low water cut off switches that work on mili volt systems?

Tim McElwain

For the McDonald Miller

67 LWCO use a number 11 MV switch for millivolts.