Hydrostat 3250

ev69

If u have it set at 140 lo 160 hi. Is ok it if it shuts down at 150 ?

Ron Jr._3

If there's a call for heat at the T-T terminals then it might shut off before it hits 160. Depending on the internal settings

HVACNUT

When you say "shuts down", do you mean the burner runs until the temperature reads 150°, or the burner stops at 140°, but boiler temperature continues to climb to 150°?

What is "Economy" set to?

Temperature will vary, depending on the settings. As long as the temperature doesn't significantly rise above the High Limit setting.

I believe it has a 10° fixed differential.

EdTheHeaterMan

Are you using it on a boiler that has a tankless coil? if not, you set the low to OFF. If you are using a tankless coil for DHW, then the 140° setting to maintain a minimum of 140° in the boiler WILL cause the boiler temperature to go above 140° before the burner stops. And 150° is not unreasonable. The burner will start as soon as the boiler temperature drops to 140° in order to maintain the minimum 140° setting. That is because the differential on the control is additive.

If you had a subtractive differential control, then to get the same result, you would need to set the control to 150° with a 10° differential in order to maintain the 140° minimum.

Big Ed_4

Is there any way to maintain a higher temperature then 140* for a domestic coil using a auto mixing valve ?

EdTheHeaterMan

Tankless Coil DHW MUST always have a mixing valve. It is just something the installer does not always do because they don't understand how a tankless coil works. There is always that possibility the boiler water WILL get to 200°F during the course of a normal central heating cycle. If no hot water is being used durning that cycle, the DHW inside that coil will get close to that 200°. If that water is then allowed to exit a tap without going thru a mixing valve, then the person that is near that tap will get some room temperature water for a few seconds until that 200° water reaches the tap. The elderly, or a small child that does not have the necessary reaction time will surly get burned by 200° tap water.

So to answer your question @Big Ed_4, YES, you can increase the low limit to 160° and the high limit to 180° or higher in order to get more DHW capacity. My default settings on a tankless triple aquastat is 160° LO. 180° HI. 10 DIF.

If you ever find an operating tankless coil on a boiler that is also used for central heating, I would tell the customer that it is unsafe to operate the boiler the way it is piped and they need to have a plumber install a mixing valve. if they indicate that they are not going to do that, I turn off the switch and leave a note on the work order "Scalding Hazard. Left Switch Off. Operate at your own risk"

And tell them to turn the switch on at their own risk after you leave.

Big Ed_4

I noticed on the Hydrostatic the low limit could not be set higher then 140* and there is no adjustment on the diff … I wonder if locked setting could be bypassed ?

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1812690#Comment_1812690

Remove jumper B to set the LL higher than 140°.

Differential varies.

Big Ed_4

Thank You for clearing it up for me …..