Aquastat Breakdown: What You Need to Know 

Increase in temp on a boiler You need to decrease pressure on the water pressure valve this is done by turning screw counterclockwise around 10 to 15 lbs is good working pressure is achieved at max temp set by aquastat set to about 200deg depending on your heating needs

Yes, install it. 👍

There are actually THREE differentials on a triple aquastat. Two of these diffs are hidden and fixed at 10 degrees, the third diff is adjustable with the DIFF control. As far as I know I am the first person to state this fact explicitly. Every other source I've watched or read throws around the word "differential" imprecisely without pointing this important fact out. Here are the three differentials. 1. First diff determines when burner turns ON for domestic hot water. LO setting minus fixed differential of 10 degrees. When water temp goes 10 degrees below LO setting the burner turns on to make domestic hot water. The burner ALWAYS turns on at 10 degrees below LO, this is not adjustable. Example: LO set at 140. When water temp cools to 130 burner turns on. 2. Second diff determines when burner turns OFF for domestic hot water. LO setting has an adjustable DIFF (DIFF can be set at 10 to 25 degrees). Example: LO set at 140, DIFF set at 25. When water cools to 130 burner turns on (see 1 above). Burner turns off when water reaches 25 degrees above this low point, or at 155. The second function of DIFF is the temperature above which the circulator pump will be allowed to circulate hot water to the radiators on a call for house heat. This is so anyone taking a shower does not feel a sudden temperate drop from heat being diverted from the shower to the radiators. In this example the circulator will not be allowed to turn on below 155. 3. Third diff determines when burner turns ON for heat. HI setting minus differential of 10 degrees (fixed). When the house thermostat calls for heat the burner turns on at HI minus 10 degrees and turns off at HI setting. Example: HI set at 180. On call for heat burner turns on at 170 and circulator is allowed to run. Burner turns off at 180 but circulator keeps running until house thermostat temp is reached. In warm weather when house is not calling for heat the HI setting never gets reached and the boiler only uses the LO and DIFF for domestic hot water. More details here: @t Additional notes: HI and LO must be set at least 20 degrees apart. Less than 20 degrees and the circulator might not ever be allowed to circulate heat to the radiators. Example: LO set at 170, DIFF set at 25 HI set at 180. 170-10+25 = 185 is the temp at which circulator is allowed to turn on. But HI of 180 means water will never reach that temp. So the burner will just run and heat water to 180 and the radiators will never get hot. Any comments or feedback appreciated. It has taken me a long time to figure all this out. I'm not an HVAC guy, just a homeowner with an oil burner who wanted to understand it. Even this video does not explain this clearly.

Do you have a video of how to wire it in with the circulator pump?

Thanks for the video. What about the differential setting? I have an oil burner tankless coil. Would it be better at setting closer to 25?

Thanks for this video. What is the failure rate for a Honeywell Aquastat? Ours won't trigger the pump. The thermostat turns on the boiler. I put a dmm to the electrical output of the aqua stat that feeds the pump and there is 0 Vs. Thanks again.

Thanks.

Thanks! I was told that the water temp. cannot be turned down when I knew the difference. Now the seals in the taps are melting everywhere and her washer is ruined. The company that installed my Mother's new furnace probably just wanted to take advantage of her by getting them to come back over and over. That pisses me off...big time.

how i can wiring i run one feed from the panel ! the l6006c 1018 + cartridge circulator + swicht ?

If your relief starts leaking on a pressurized system you may want to ensure your pressure is less than the relief psi. Over filling. Bad expansion tank etc. Could be culprits rather than just temperature.

How do you service an Aquastat on a John Woods oil fired hot water heater? Do I need to drain the tank?

There is water leaking from my CONTROL well. Can I just replace it or is there more of an issue there? Thanks

I have a Honeywell digital aquastat. My boiler does domestic hot water and baseboard heating. I have a problem where am I domestic hot water is scolding hot. What setting should I adjust to make this lower? Thank you

I am using this with a RUUD hydronic air handler. I have a wells McLain boiler. So the thermostat calls for hot water from boiler, sends to air handler. The AQUASTAT turns on the air handler when pipe is hot enough. What temperature should AQUASTAT be set at, along with differential setting? The air handler seems to turn in and off frequently, even when thermostat is call for hot water from boiler

Could you do a video on the actual wiring. I mean actual. Don't just show wiring aquastat but where cables come from and where they go. Thanks

Installing electric tankless hot water heater. I was told to add an aquasat before the water heater and circulating pump to achieve quick hot over long shower. Does adding an aqua stat affect the boiler in any way?

You miss something, the location of aqua stat on coil furnace in order for the blower fan to operate properly. Is it in the supply line or return line from the coil

Do I need to drain the whole radiator system before changing the Aquastat? I have yet to see a video changing on of these.

I know nothing about my boiler except that it’s a Honeywell and we are forced hot water and we did have an added water tank. Our boiler was running all the time and it was running over the hot temperature. We had it serviced and they said it was nothing wrong with it. I read on another forum that the set on my walls and the ghosting could be from my boiler. What do you think about that? May I please add one more thing? And your video I think your singing people know what you’re talking about, you should be up closer on the video so we can see what you’re pointing at and maybe show us where the aquastat is located. Lol thank you so much.

Mine is like the image you inserted at 2:50. So, the variable differential which, as I understand it, is in degrees above the wired in 10 degree (in mine) differential below the set low limit, ( a set low limit of 160 has a low differential of 150 making a set differential of 20 deg to be 170), governs the temp at which the circulator will come on, assuming there is a call for heat? So what if it is warm weather and no heat needed; boiler just falls to 10 deg below set low limit, back up to set differential, then back down? These things are not that simple and I may have to edit this comment.

My water will not heat up. The system is 25 years old. I was told the old thermostats have a contact point system and it may just need some cleaning. I thought I cleaned them but not sure. Any video of how to do this? Thanks

Your sentence "When boiler temperature is rising: on an aquastat control, the differential control dial specifies the amount above the "Low Limit" where boiler temperature must rise before the burner will turn off and the circulator will be allowed to run and send heated water through the system." - the circulator will only come on if there is a call for heat, correct? And if there is a call for heat the burner will stay on? The burner will turn off when the differential is reached only if there is not a call for heat?

Any videos on wiring 3 circulator pumps for 3 zones

Need wiring info

How do you wire Aquastat to operate a fan for a garage heater?

how is the wiring

Ispanihs plis

Isn't this referred to as a high limit aquastat only?? This isn't a typical aquastat that we find in homes with a high and low range, it keeps the boiler in a range that hot water is always ready. The type you are showing only warms up the water when the thermostat calls for room temperature heat, it sis not used with tankless hot water systems...

Didn't learn much, other than over heating my boiler, maybe my aquastat is trash

There are actually THREE differentials on a triple aquastat. Two of these diffs are hidden and fixed at 10 degrees, the third diff is adjustable with the DIFF control. As far as I know I am the first person to state this fact explicitly. Every other source I've watched or read throws around the word "differential" imprecisely without pointing this important fact out. Here are the three differentials. 1. First diff determines when burner turns ON for domestic hot water. LO setting minus fixed differential of 10 degrees. When water temp goes 10 degrees below LO setting the burner turns on to make domestic hot water. The burner ALWAYS turns on at 10 degrees below LO, this is not adjustable. Example: LO set at 140. When water temp cools to 130 burner turns on. 2. Second diff determines when burner turns OFF for domestic hot water. LO setting has an adjustable DIFF (DIFF can be set at 10 to 25 degrees). Example: LO set at 140, DIFF set at 25. When water cools to 130 burner turns on (see 1 above). Burner turns off when water reaches 25 degrees above this low point, or at 155. The second function of DIFF is the temperature above which the circulator pump will be allowed to circulate hot water to the radiators on a call for house heat. This is so anyone taking a shower does not feel a sudden temperate drop from heat being diverted from the shower to the radiators. In this example the circulator will not be allowed to turn on below 155. 3. Third diff determines when burner turns ON for heat. HI setting minus differential of 10 degrees (fixed). When the house thermostat calls for heat the burner turns on at HI minus 10 degrees and turns off at HI setting. Example: HI set at 180. On call for heat burner turns on at 170 and circulator is allowed to run. Burner turns off at 180 but circulator keeps running until house thermostat temp is reached. In warm weather when house is not calling for heat the HI setting never gets reached and the boiler only uses the LO and DIFF for domestic hot water. More details here: inspectapedia.com/heat/Aquastats.php Additional notes: HI and LO must be set at least 20 degrees apart. Less than 20 degrees and the circulator might not ever be allowed to circulate heat to the radiators. Example: LO set at 170, DIFF set at 25 HI set at 180. 170-10+25 = 185 is the temp at which circulator is allowed to turn on. But HI of 180 means water will never reach that temp. So the burner will just run and heat water to 180 and the radiators will never get hot. Any comments or feedback appreciated. It has taken me a long time to figure all this out. I'm not an HVAC guy, just a homeowner with an oil burner who wanted to understand it. Even this video does not explain this clearly.