do i need the aquastat

amateurplumber

i have a burnham V904A gas boiler that gives steam heat and for hot water production it pumps to a coil in a hot water storage tank. the building is an 8 unit apt building in brooklyn ,ny.

it is my understanding that the boiler is turned on and off by the aquastat on the hot water storage tank (set at 150)for the production of hot water and by the pressuretrol for the production of steam heat.

what is the purpose of the aquastat on the boiler itself (set at 220).?

is it there to anticipate that the hot water aquastat is soon to be satisfied and thus the boiler can be shut off a little earlier and thus fuel is saved. is this because there is a lag time between when the boiler water gets hot enough and when the pump delivers that water to the hot water storage tank.?

although if it is at 220 i am wondering if it ever actually comes into play at all.

lchmb

guessing

It may be a high limit for the hot water production. That way the unit does not begin making steam on a call for hot water only...If the tank was to have a long call and the unit only had the pressuretrol to shut it down you could start heating the building....in July..

amateurplumber

plausible guess

yeah that is a good point , that seems like a plausible theory

Joseph_4

could be required

also guessing... In NYC you need a backup aquastat when in a multi family dwelling for a forced hot water heating system. Honeywell's backup aquastat has a red button that needs to be manually reset if it goes off on limit so the problem is rectified and not just put back on line. could be its required for domestic hot water as well

Joe

amateurplumber

there is an emergency aquastat too

there actually is a second aquastat on the boiler that is a honeywell with the red reset button just like you mentioned. it is set at 255.



i made an error in my original post. the (non high limit )aquastat on the boiler is set at 180 not 220 and the aquastat on the hot water storage tank is set at 140 not 150.

lchmb

so

Either the boiler is set to maintain temp (180) through that aquastat or when the boiler is called on that works as a high limit if done for domestic hot water..either way it's needed...

Jean-David Beyer

honeywell with the red reset button just like you mentioned. it is set at 255.

I am not a professional, but if that is a water boiler, I sure hope that aquastat is 205 or less, because you do not want that water ever to boil.

lchmb

actually

JDB, he does want it to boil..it's a steam system..;)

Joseph_4

any pictures?

do you have a hydronic heating loop running off the bottom of the steam boiler. 180 and 255 backup dont make much sense. if you have a pressurized hydronic loop well when hot at 20 psi boiling point is 259F. 180 is normal hydronic temp, way too hot for domestic hot water. Also, the aquastat on storage tank probably controls circulator, not there to fire boiler. does boiler have coil. Pictures would really help.

Jean-David Beyer

OK, I missed that it was a steam system.

I know even less about steam systems than I know about hot water ones. My grandparents had a steam system, but I was just a kid when I saw that. And I did not know what to look for..



So 255F seems to give a pressure of about 20 psi (gauge pressure) which I suppose is an appropriate safety limit for such systems, right? From what I read here, I infer that that you would not run the system that high, but we are talking about an emergency backup, not the normal operating cotnrol.

amateurplumber

emergency aquastat

i assume the plumber knew what he was doing when he set it to 255

amateurplumber

pics and wiring diagram

i dont know what a hydronic loop is or looks like. here are some fotos. according to my analysis of the wiring the aquastat on the hot water storage tank does control the burner (and the circulator pump). boiler used to have a coil when it heated the hot water direct a few years ago , but it was removed when we switched to the current indirect system and now the only coil is in the hot water storage heater.

Abracadabra

Maybe..

I used to see boilers around here with aquastats on the return line, setup to prevent boiler from quickly firing again after it just went thru a cycle.  If the boiler had just gone thru a cycle, the radiaotrs were hot, the aquastat qould wait until return line cooled a bit before allowing the boiler to go thru a cycle again.

Eric_32

the aquastat...

on the indirect tank should be set to the temp of the potable hot water.

The indirect is sending the signal to the circulator and  burner to run for hot water. The burner should be getting powered thru  that aquastat on the boiler near the old abandoned tankless coil in your picture, and that should be set to 180°F as a hi-limit control for the burner so it doesn't make steam on a call for hot water and heat the house.