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Thread: Aqua Stat Trouble?

  1. #1
    DIY Senior Member bbillcee's Avatar
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    Default Aqua Stat Trouble?

    I have a weil mcclain boiler with a coil and separate hot water heater. In the spring i shut down the boiler and turn on the hot water heater....

    i started up the boiler for the winter and when i go to use the shower the water will come out hot for a min or too then turn cold.....after letting it run for a few minutes the boiler kicks on the water warms up.

    it is my understanding that the aquastat keeps the boiler water to whatever it is set to. mine is set to 160


    i have a hot water guage (it appears to work) that shows the water around 80 degrees in the morning when no one has used hot water all night, The guage is a bout 4 feet away from the output pipe of the coil.

    could it be my aquastat is faulty?


    also i would like some thoughts on running the output of the coil to feed the input of the hot water heater and keep the hot water heater on all year round.....this coil is nothing but problems but maybe it could keep warm water going into the hot water heater to be more efficent?


    thoughts?
    Last edited by bbillcee; 10-18-2007 at 04:03 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Is the separate WH on all of the time? How is the boiler involved? Not clear to me. Some boilers are better at domestic hot water than others since they can handle cold starts (cold return water) better than others. On some the shock of huge differentials can damage them. If your boiler can handle the cold starts well, and doesn't have much standby losses, it's a good candidate for an indirect WH tank. If the coil in the boiler makes the domestic hot water by an imersion process, then there will always be a delay unless it maintains the temperature required to produce that hot water. If the boiler is supposed to maintain 160 always, and it is down to 80, then it may be the aquastat.

    An indirect tank may be cheaper to run, but adding the zone and buying and installing may take a long payback period. They work well, though.

    If you dont' go that route, using the boiler's imersion system to preheat that going to the WH during the heating season would save on the fuel used in the WH. Typically, a boiler is more efficient than a fire-ed WH. An electric one is about as close to 100% as they get, though.
    Jim DeBruycker
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    DIY Senior Member bbillcee's Avatar
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    the WH is only on in the summer months I have it piped independent of the boiler.. the coil on the boiler supplies the domestic hot water in the winter months and i shut down the WH

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Do you drain and bypass it?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member CHH's Avatar
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    To address the original question: If the boiler is supposed to be maintaining at least 160 degrees and it isn't (but otherwise functions normally) then it's time to test the aquastat. You should be able to test it using a thermometer and electric continuity tester/multimeter and a pan of water on the stove top.

    Using the coil inline ahead of the water heater should be fine. About the only potential problem would be if the coil limed up but that can happen now.

  6. #6
    DIY Senior Member bbillcee's Avatar
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    i do not drain it but i bypass the hot and cold inlets with valves

    can u describe a bit how i can test the aquastat with the meter and therm?

  7. #7
    DIY Senior Member CHH's Avatar
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    The aquastat is just a temperature activated switch which probably has 3 terminals. It's handy to have the manual for the stat.

    Basically the stat will make or break circuts based on temperature. So put the temperature sensor in the pan of water (maybe use a double boiler to keep the sensor dry) and watch continuity between the terminals as the water is heated. The low temperature limit should probably be closed (show continuity) for temperatures below the set point. If you can't find any continuity below the set point then inspect the contacts and clean'em (if you haven't cleaned them already). If cleaning doesn't work then plan on replacing the stat.

    If you've ever tested a engine thermostat it's the same concept but the meter is required since you can't just see the thermostat open and close.

  8. #8
    DIY Senior Member bbillcee's Avatar
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    is the temp sensor directly in the boiler water? whats steps need to be taken to remove it?

  9. #9
    DIY Senior Member CHH's Avatar
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    The temperature sensor is probably in a dry well. There is probably just a retaining screw holding the stat to the dry well.

    Mark or label the wires so re-attaching them correctly will be easy. Be sure all power is shut down prior to working on the boiler. The stat should only have 24 VAC on it but it could be set up with 110 VAC.
    Last edited by CHH; 10-18-2007 at 11:07 AM.

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    A typical aquastat is just a temperature controlled switch, but you mentioned that you have a readout on the boiler showing the current temperature. It is possible that the system does not use an aquastat, but an electronic control fed from a thermistor (i.e., an electronic thermometer). If that is the case, it could be the control board, a sticky relay (controlled by the control board), or be an independent thing, and an aquastat (switch) is supposed to control the operations. Some of those are adjustable, but many are not. Also, it is possible that the system has a flow control switch that won't activate the boiler until it senses flow (similar to a tankless heater's operation), and what you have is normal; unless the boiler was called to heat the house, it could let the storage water cool off until there was a demand. All of this is guesswork, since I don't know your system's control features.
    Last edited by jadnashua; 10-18-2007 at 11:16 AM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    DIY Senior Member bbillcee's Avatar
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    i see what u mean it just looks like a copper wire ......

    i'll see what happens!

  12. #12
    DIY Senior Member CHH's Avatar
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    There should probably be a sensor bulb on the end of that copper wire...

  13. #13
    DIY Senior Member bbillcee's Avatar
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    ok before i went ahead and took everything off i took water directly from the boiler and double checked it with another therm.....it was dead balls on 160

    so what else could cause the water to start out hot then get luke warm then be hot again when the boiler is up and running while taking a shower???

    in another words if i was to let the hot water run in the shower it would start out hot then luke warm for a few minutes (i hear boiler kick on) then water starts to heat up again
    Last edited by bbillcee; 10-18-2007 at 01:05 PM.

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    Aquastats sometimes have a dual mode. In other words, they need some hysterisis (if it was trying to decide to open or close without some gap between the open close temperature, it could chatter on/off right around the set point). So, the switch could be sticky, and let it get colder than desired before it turns back on. If you have the specs, it will probably give a range - on at some certain temp, then run until it reaches some (higher by maybe as much as 20-degrees or more) temp, then shuts off. So, yours may be set to turn on at 160, or it may be set to turn on at 140 and then off at 160, depends on whether that 160 is the upper limit or the lower limit. Could still be the aquastat, or if electronically controlled, the circuit board.

    As the days get colder, the incoming water does too. So, unless the house thermostat was calling for heat (and the boiler temp probably goes higher), you're starting with colder water and would notice it more now than in the summer when the incoming water, and thus the rise needed to have a comfortable shower, is greater. This is a typical problem with anything other than a storage system.
    Last edited by jadnashua; 10-18-2007 at 01:22 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    DIY Senior Member bbillcee's Avatar
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    thanx for all the help guys


    anyway its a honeywell aquastat type l4006a and the circuit opens when the temp goes above the set temp

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