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Will differential of aquastat clash with Tekmar 362 differential function?

Not sure if I am asking a question about a non-issue since I've yet to install this setup and actually encounter a problem, but I've currently got a gas fired hot water boiler controlled by a Honywell L8148E aquastat that I plan to modify in the near future and it got me wondering.....

As part of my coming boiler repipe, we'll be controlling the boiler with a Tekmar 362, and I plan to replace the L8148E with a Hydrostat 3100 to add the benefit of low water cutoff.

The default high temp differential on the Hydrostat is 10 degrees, and that is the minimum setting(the L8148E has a fixed 15 degree diff).

The 362 also apparently calculates differential, or it can be set manually, and this is determined by the boil, supply, and indoor temp sensors from what I can tell.

My question/concern:   Will the 362's and 3100's  differential functions acting at the same time cause any problems?  Will they "clash" or otherwise step on each other, or are they really somewhat independent and not an issue?

It seems like one would have this scenario anyway with any aquastat and its differential setting, unless it can be set to zero.  So perhaps this is a non-issue and the 362 takes this into account?

But as I read the documentation on the 362, it got me wondering.


Just a DIY'er trying to learn, and improve and maintain his converted ca 1929 overhead gravity hot water system since there is no one local that can.


  • Randy Baerg
    Randy Baerg Member Posts: 26
    tekmar 362 vs boiler aquastat

    The 362 control can be set to operate two different ways. If you want it to control the boiler (with differential) then set it's boiler sensor = Supply. This is typical if the only load on the boiler is the mixing device. The 362 will now become the 'boiler operator'. Your boiler aquastats should be set up higher than any target the 362 would be trying to fire the boiler to. Usually 20°F higher should work. E.g. tekmar 362 target = 180°F then boiler Aquastat = 200°F and high limit to 220°F. In effect you have two high limits.

    The other set up is to have the 362 just enable the boiler. This is typical if their are other loads on the boiler other than just the mixing. In this case set the 362 boiler sensor = Return. The 362 will now just hand off boiler operation to the existing boiler aquastats and they would be set normally. E.g. operator 180°F, high limit 210°F.   
  • Al Roethlisberger
    Al Roethlisberger Member Posts: 194
    Thanks Randy, that's what we arrived at as well.

    Thanks Randy, after some other discussions that is the conclusion we arrived at as well and will be sensing the supply side and just build in the buffer differential of 10-20F between the high limit on the 362 and aquastat, the aquastat being set higher.

    Much appreciated!

    Just a DIY'er trying to learn, and improve and maintain his converted ca 1929 overhead gravity hot water system since there is no one local that can.
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