Problem with Aquastat Tripping


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Old 01-05-23, 12:13 AM
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Question Problem with Aquastat Tripping

I'm helping to troubleshoot a hydronic radiant heating system for two apartments. There is a single boiler with two Honeywell aquastats wired in series. One is a L4006E with manual reset. The other is similar but has no manual reset. They both are set to about the same temperature, 180 degrees.

I reset the resettable aquastat and let the system heat up for about an hour. One apartment with occupant had its thermostat turned on. The pump seemed to be running and the temperature of pipe feeding that apartment was about 110 degrees. The occupant seems to enjoy heat, at least for a while. The thermostat in the other apartment was off and its pump remained off and pipes were cool.

Reportedly, the aquastat with manual reset periodically trips, maybe in several days or so, possibly worse when the apartment thermostat reaches temperature. The occupant then no longer gets heat.

What could be the problem and how should I troubleshoot it?

Why does the temperature of the heated water pipe not rise to 180 degrees? Are the temperature settings for the aquastat incorrect? Should the one with the reset be at higher temperature, maybe 220 degrees? Could that aquastat be defective?

Thanks.
 
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Old 01-05-23, 01:57 PM
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The manual reset control should be 30 - 40 degrees higher than the auto reset control. If this is a newer boiler it is not unusual to see a residual buildup after the heat demand goes away of 20-30f.
 
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Old 01-05-23, 04:02 PM
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It looks like what they have done although both aquastats were wired in series one would operate the boiler and the other with the reset would act as a safety in case the 1st malfunctioned and wouldn't shut the boiler off causing potentially a very dangerous situation.

As rbeck suggested the aquastat with the reset would shut the boiler down and would have to be manually reset to regain operation. If that reset activates then that is telling you that the 1st is working correctly and should be replaced.

I would follow rbeck's suggestion and set the 2nd aquastat @ 220 deg. and your problem would be solved.

I noticed a couple of other posts about the same time so just a final thought. Although DH's suggestion would work it does not have a manual safety built in. From what you said this is not an owner occupied residence, and not constantly checked so having that safety of the manual reset is a good thing to have.

Hope this helps a little.
 
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Old 01-05-23, 09:59 AM
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HelpfuD: Why does the temperature of the heated water pipe not rise to 180 degrees? Are the temperature settings for the aquastat incorrect? Should the one with the reset be at higher temperature, maybe 220 degrees? Could that aquastat be defective?
Many heating problems are due to poor control of boiler water temperature. Old bulb sensing control ie. Honeywell L002 cost $ 196 can be off by 10 or 20 F from setting and do not display actual measured temperature. https://www.supplyhouse.com/Resideo-...e-Manual-Reset

Another issue is temperature gauges on boilers are often inaccurate and make trouble shooting difficult.

An $186 aquastat with 1F degree control, live display of actual temperature, menus for hi low settings is Tekmar 256. Also has saves up to 20% on fuel cost with out door reset. Read the Submittal and Install links to see major benefits:

https://s3.amazonaws.com/s3.supplyho...-submittal.pdf

https://s3.amazonaws.com/s3.supplyho...56-install.pdf

https://www.supplyhouse.com/Tekmar-2...iler-4150000-p

On existing systems with multi function aqua-stats, the two wire contacts on Tekmar 256 can be used instead for temperature control while other multifunction's still remain in use. The small Tekmar sensor 1/4" x 1" can slip in well behind L003 bulb or just outside it. Does not require immersion, just physical contact.
 

Last edited by doughess; 01-05-23 at 12:03 PM.
  #5  
Old 01-05-23, 03:20 PM
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With any aquastat technology, when max setting is reached and turns off boiler, residual heat In chamber continues to raise the water temperature.

When DH Tekmar 256 aquastat, which displays 1F, was set 180F, boiler water continued to rise another 10F to 190F. Since 180F is recommended max, changed Tekmar max to 170F to avoid boiler scaling.

Most modern boiler use these accurate electronic controls to maximized benefits. Old L002 control are chronic source of problems and higher heating costs.
 
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Old 01-05-23, 04:00 PM
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What is the boiler pressure when cold? Are the 2 apartments at the same elevation? The aquastat with manual reset is for the high limit control. The high limit control protects the boiler. If it trips it means the water temperature in the boiler has exceeded the adjustable high limit setpoint on that aquastat. After the water cools below the high limit setpoint, manual reset can occur. The aquastat witout manual reset also has an adjustable high limit setpoint for high limit. After it trips on high limit, it will automatically reset after a cooldown below its high limit setpoint . The water temperature at high limit trip should be close for both aquastats. The contacts in each aquastat associated with the high limit setpoint trip must control a common voltage that prevents either aquastat from firing the boiler.
 
 

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