Aquastat accuracy

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Old 01-27-08, 01:41 PM
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Aquastat accuracy

Is there anyway to check the accuracy of your aquastat and boiler temp. / pressure gage…neither seems to be accurate.
Mark S.
 
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Old 01-27-08, 02:14 PM
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One has got to fairly accurate. Maybe they both are. If the gauge and control are not in the same place they will read differently. If the height is different or in different sections or one in a pipe they will not and cannot read the same. I have seen differences of 15-20 degrees and both were accurate.
 
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Old 01-27-08, 05:12 PM
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Temperature/Pressure Gauge

Rbeck pretty well covered the temperature part. To check pressure, you can get a gauge from most home centers which will screw onto a hose bib on the boiler. Just install the gauge & open the hose bib.
 
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Old 01-27-08, 05:24 PM
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The thing I don't like about them is that the gauge is either gonna be 0-200 PSI or 0-300 PSI ... I can't imagine what Watts is thinking ?! Does ANYONE have a water system that will produce that much pressure ? (these are intended for use with sprinkler systems, but work for boilers too). The gauge resolution is pretty p!$$ poor for pressures under 40 PSI.

The brass fitting is pretty nice, and takes a standard NPT thread for the gauge. So, for a few bucks more, pick up a 0-50 or 0-30 PSI gauge at the plumbing supply and replace the one that comes with the unit.
 
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Old 01-27-08, 06:12 PM
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I have a Weil Mclane WTGO -4 although I no longer make DHW with the coil. I have an indirect fired DHW tank. I was just asking because the high limit is set at 180 degrees but when the burner shuts down on high limit the temp gage reads around 210 degrees… thanks for your thoughts.

Mark
 
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Old 01-27-08, 06:36 PM
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Mark, if you are seeing that temp minutes after the burner shuts down, and the heat call is finished, the circ has stopped, it's probably from 'heat soak' ... the heat trapped in the boiler iron is transferring to the water.
 
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Old 01-27-08, 06:51 PM
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I haven't looked for a while but I think that you can pick up pressure gauges that are 0-60 psi in the pumps section of the big box stores. All you need then is a 3/4 to 1/4 bushing and the 3/4 inch pipe to hose thread adapter. Any plumbing supply store should have a number of gauges in whatever range you desire.


As for "accuracy" in thermometers, pressure gauges and aquastats...most are manufactured to a fairly "loose" tolerance of one-to-two percent of the full-scale reading. Rough handling can easily jar them from absolute accuracy. Far more important than absolute accuracy is repeatability, that is the ability to indicate (or in the case of the aquastat, actuate) at the same point whenever the same temperature or pressure is sensed regardless of whether or not the indicated pressure or temperature is exactly correct.
 
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