Question about the boiler temperarture control micro-switch

[super80]

I have question of those temperature control setting about my boiler, there're 3 tempererature sensor switch on my boiler system, 2 located next to the boiler and the other one is located on the storage tank.
Those two near the boiler set to 140F and high limit is set to 210F, so I'm wonder to know what setting I need to set the one that located on the storage tank?? and what is the 140F and 210F setting mean?? do they mean the boiler "heat up" water to 210F then if water temperature drop to 140F, then boiler heat the water again?? am I right? if so what is the use of the one that located on the storage tank??
thanks for helping!!

[MSKLAUNDRY.]

The 210 is the hi limit in case the others fail or something else goes wrong with the boiler such as the circulation pump failure or other fault. The red plunger on the control will pop out. Usually the hi-limit should be set to about 40 deg higher than the water temp. The one on the tank provides a more precise control of the actual water temp but it really isn't necessary and in most installations is left out.

[super80]

The 210 is the hi limit in case the others fail or something else goes wrong with the boiler such as the circulation pump failure or other fault. The red plunger on the control will pop out. Usually the hi-limit should be set to about 40 deg higher than the water temp. The one on the tank provides a more precise control of the actual water temp but it really isn't necessary and in most installations is left out.

any recommendation on the setting of the one that located on the tank?? if the setting of the other control which next to the high-limit is 140F.
thanks!!

[MSKLAUNDRY.]

Set it at the temp you want your water to be at. 120 deg should be acceptable for most laundries.

[super80]

Set it at the temp you want your water to be at. 120 deg should be acceptable for most laundries.

did you mean set "BOTH" temperature micro-switch to 120F, then high-limit set to 160F, right??
thanks for helping!!

"BOTH" means the one that sitting right next to the high limit and the one that located on the storage tank..

[MSKLAUNDRY.]

Yes, set the hi limit 40 deg higher than the aquastat. The aquastat to 120 deg and the other thermostat slightly higher than the aquastat, say 130. (It really down't matter since primary control will be the aqaustat). As long as it is above the aqaustat it will let the aqaustat do the control of the water temp.

Note: I have seen some crazy wiring by plumbers/HVAC people so this may not be correct for your situation. Its not like anything bad will happen but it may not react as I say it will since I don't know how the aqaustat is wired into the heater. Before changing anything may a note of where the settings are.

[super80]

Yes, set the hi limit 40 deg higher than the aquastat. The aquastat to 120 deg and the other thermostat slightly higher than the aquastat, say 130. (It really down't matter since primary control will be the aqaustat). As long as it is above the aqaustat it will let the aqaustat do the control of the water temp.

Note: I have seen some crazy wiring by plumbers/HVAC people so this may not be correct for your situation. Its not like anything bad will happen but it may not react as I say it will since I don't know how the aqaustat is wired into the heater. Before changing anything may a note of where the settings are.

does the "aquastat" means the one that located next to the high-limt?
if so, I can tell you that the one that located on the tank seems override the control of the water temperature, because my current setting of both are aquastat set to 140F and tank is set to 150F, but the heater don't stop heating until the water temp. up the about 150F, and comment on this?? is that like what you said wrong wiring by plumbers, any solution on correct wiring problems??
thanks for helping

[mjwalsh]

I wonder if your temperature switches (aquastats) are the older style where you are stuck with more temperature differential than some of the newer controls where you can specify a more precise differential. Of course there may be an issue of more cycling on & off if a newer control is set to too little differential.