Honeywell Aquastat Triple relay wont turn on Circulator pump

Old 01-14-18, 10:58 AM
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Smile Honeywell Aquastat Triple relay wont turn on Circulator pump


Recently I fought a battle with a problem on my heating system.

Oil burning hot water boiler with 3 zones and raditors pushing Hot Water.

The number two circulator pump is controled by a honeywell aquastat triple relay. the problem was the furnace would come on however the circulator pump would not.

The aquastat supplies 24VAC to the thermostat . so the thermostat is a simple SPST switch to the T1 and T2 terminls on the aquatstat. Thus shorting T1 and T2 should bring the furnace and cirulator pump on.

I had two HVAC guys tell me the Aquastat was bad and that was why the boiler came on but the circulator pump would not,
T1 & T2 shorted ( closed) the K1 relay would click (closing contacts) C1 and C2 should now have 120VAC to run the circulator pump but did not

I was seeing zero volts at C1 and C2 with K1 relay closed by closing (shorting) T1 and T2

After 2 refurbished Aquatstats that did not work and 1 New Aqaustat that stopped working after one month i became frustrated , so I took the old Aquastat to task. By making a bench setup to supply 110vac to L1 and L2, a switch across T1 and T2 and a 110 light across C1 and C2 . I now had a test set up.

After checking continuity, volatge and circuit path with K1 closed by shorting T1 and T2 I had zero volts at C1 and C2 ( circ Pump). Altimaltly I found that the low level limit finger switchs were out of calibration. The Low Limit switch know on the white box has a miminum setting of about 110 degrees and upper limit around 200.
Inside the white box is a threaded post that sets these low limit contacts opening and closing. This shaft can be screwed in and out. When the white box cover is on , the knob has stops giving you maybe 3/4 of a turn of low limit . In my case by turning that shaft untill I had a closure and 110 vac at C1 and C2 fixed this. Then with the cover closed I put the knob back on with the pointer set at the 120 mark when the furnace had cool to one 120. The Aquastat now functions as it should and the circulator pump comes on.

That is to say that with T1 and T2 shorted , The K1 relay closes and we see 120vac at C1 and C2.

This is a saftey issue and there is more to calibrating this then I can describe here. So the method I described here was just a summary for information not a complete discussion. Consult a trained professional.

In closing :
for a honeywell Aquastat triple relay with the symptoms of Everything works but the circulator pump will not come on . WIth you thermostat set for a 80 degrees calling for heat or a contact across T1 and T2 you should see relay K1 close and C1 and C2 have 120 VAC. If not have your HVAC Tech suspect calibration of the LOW TEMP LIMIT adjuster, not a broken Aquastat triple replay. He may be able to adjust the shaft instead of replacing the $150 -$200 Aquastat relay
Old 01-15-18, 09:41 AM
Join Date: Apr 2014
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These multi function Honeywell aquastats make life extra difficult when there is an issue. They are cheaper and easier for contractor to install....but. There is an old saying about all your eggs in one basket. Like eggs, when of of these when one breaks it can be a real mess.

I use a Tekmar 256 out-door-reset (saves 5% to 15% in fuel costs) as aquastat with far more features than older dumb ones. Have separate control for circulators. Use a high and low limit temperature control for boiler max temp and circulator low temp 137F cutout.

Have pilot lights on everything to know what is going on. On cold winter nights do not want or need diagnostic challenges, just heat.

Last edited by doughess; 01-15-18 at 11:44 AM.

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