Aquastat Low Limit

litedesign

Seems like almost every aquastat out there for sale has a high limit and a low limit function. Curious to understand what situations you would need a low limit to override the thermostat and keep your boiler water above a certain temperature (140ºF?). I've read a lot of information about condensation, corrosion, short-cycling, etc.

Does every boiler need to be kept above a certain temperature to avoid long term damage? Or is this just for specific situations when you're using the boiler for hot water and heat?

STEVEusaPA

Hi and Lo are usually called triple aquastats. Lo limit is used to keep the boiler at a minimum temperature on boilers that use an internal coil for domestic hot water. Also used to keep the circulator off when the temperature is below the lo limit temperature.

litedesign

STEVEusaPA said:

...boilers that use an internal coil for domestic hot water.

Thank you! Can you explain that a little further? I thought domestic hot water was always provided by a hot water heater (tank or tankless). What is the difference between an electric hot water heater and a "boiler that uses an internal coil for domestic hot water?"

EdTheHeaterMan

I'll take this @STEVEusaPA . I have diagrams give me a minute

EdTheHeaterMan

A high limit control is something where the electrical contacts break on temperature rise. Like a room thermostat will open or switch off when the room temperature rises to the setting on the thermostat.

A low limit electrical contacts make on temperature rise

There are some aquastats that have a single pole double throw set of contacts where R and B break on temperature rise and R and W make on temperature rise simultaneously

@STEVEusaPA mentioned a triple aquastat relay. That is a control that has 2 aquastats and a relay in the same control box (three things in one hence triple) to operate the burner and the circulator on the tankless water heater boiler above. It is designed to give priority to the DHW

Hope this answers Your query

Now what are you looking for in an aquastat? Is it a temperature only device ...or do you need a high limit that will also operate a burner and a circulator safely?

And send pictures... we love pictures!