Aquastat help


Old 01-25-13, 10:28 AM
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Aquastat help

i have a fairly old, very basic gas boiler/radiator heating setup. Recently one of the thermostat wires somehow broke at the boiler. My friend who is an HVAC guy helped me troubleshoot and repair it. While hooking it back up, we noticed that there are 2 aquastats involved: one in the tank itself and one on the main hot water pipe coming from the tank. The one on the pipe was set at 190, and my friend determined that it probably wasn't doing anything anyway, that water in that pipe will never reach 190, and decided to leave it unhooked. Is that the correct move? My boiler seems to get hotter than 190, and it could be my imagination, but I feel like the radiators are getting hotter than before the repair.

Thanks in advance.
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Old 01-25-13, 11:25 AM
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The second one was probably an 'auxiliary high limit' and intended to stop the boiler from 'runaway' in the event that the first one failed. Quite common actually and some jurisdictions require them to be added during new installs.

My advice is to connect it back the way it was and set the secondary about 20F higher than the primary.

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