Another odd one. Fan on for 2 to 3 seconds. Then off
So, in theory this would be easy if the darn thing would do it while I’m there. It’s an intermittent and admittedly by the owner it doesn’t happen often. Says maybe 3 times a day. Maybe 1 or 2. I suspect more but it goes unnoticed or they are sleeping, etc. It has no error codes, doesn’t lock out, and runs fine besides this issue. It’s never making it to ignition trial. So it’s shutting off so quick it doesn’t get a chance to lock out. I did shorten the fan on valve off time to see if we could get it over into the ignition step before it shuts off. But it’s just gonna tell me the wrong issue most likely if I force it over to fire off early.
so, what do we think. Thermostat? May have to put a darn game camera on the zone controller and the pressure/temp gauge to see where we are in the cycle and which thermostat is calling. But they say it’s really fast. So not sure I’ll catch it. I should be able to see what stat is calling though.
Beckett AFG, R7284 primary. No smart stat transformer / kit -involved. Just the primary as normal. All else is good.
Comments
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What fan are you talking about? Furnace? Boiler? Draft inducer, burner motor or indoor fan.
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Sometimes when a zone is running, the boiler will make limit and shut off the burner while the circulator keeps running. Once the Aquastat makes the High limit differential, the burner goes to start again. But the burner doesn't get far because now the thermostat satisfied and boiler temperature is between the high and low settings, so it shuts down again. Widen the High differential.
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great response. I figured something in this line but appreciate the detailed break down but easy to follow. Thank you.
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Squirrel cage actually. Not really a fan per say. So basically the burner motor.
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The burner fan and the oil pump are both operated by the burner motor. So calling that motor a fan is kind of confusing.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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If it is a mechanical t-stat and the aquastat closing drops a load on the t-stat that wasn't there before then that will start heating the anticipator faster and make the t-stat end the call faster. you may need a relay to get rid of that behavior.
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bad habbit. Can’t shake it. Even though I’m def well beyond the point of calling it the wrong name. I built the habbit being around people calling it that - made it easier to use the terminology cause I knew what they meant. But then built the habbit myself. Yea the A-stat is calling and causing the flame control / primary to fire off the motor and then some times rarely even before the pump gets up to speed and pump solenoid lets fuel hit the nozzle it shuts off. But generally it does flame off then run a bit and stop. It’s not traditional short cycling though. It’s not consistent really but does it often enough I heard it do but I was in another room replacing a T stat didn’t get there in time / didn’t know that was gonna be one of the times it did it. It runs normal a lot. I wonder is the a-stat temp sensor beginning to fail / malfunction but slowly - which I’ve not seen a slow gradual failure before but doesn’t mean it don’t happen???????? It’s not a real big issue at moment. It’s -40F right now so not gonna touch anything that isn’t a hard failure at this time. Wait for warm snap to play with odd but not emergency issues. 👍 I do have all the parts on the unit top to bottom so if it fails I’ll get over there. 👍
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