Odd very short cycle

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Old 11-25-16, 10:30 AM
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Odd very short cycle

Setup: Hydronic, 3 heating zones, 1 DHW zone. Honeywell RTH7xxx thermostats, Beckett AquaSmart 7600 (cold start). Taco SR503.

My favorite chair is near the FR thermostat (yes, the clicking is annoying) and I can also hear the boiler fire - it's almost underneath me.

I'm noticing that the boiler will fire, and then about 4-8 seconds later, the thermostat clicks off, and the boiler stops firing. It doesn't happen all the time, but I notice it a few times every day. I know what you're thinking - this is somewhat of a random act; the boiler fires when it has to (based on my aquastat settings and current heating demand), and the room reaches temp and the thermostat reacts as required. They really don't know about each other, so this could happen. Except, it happens often. Fire for less than 10 seconds, thermostat clicks off, boiler shuts off. Multiple times a day, day after day. I know that the other thermostats are not calling for heat when this happens because the boiler should continue to heat up if they were, even if FR thermostat stops calling for heat.

I've futzed with the thermostat settings (CPH), boiler diff (not sure why), etc. I've checked and double-checked all wiring per Beckett and Honeywell documents. I've convinced myself that this happens frequently enough not to be something random, but I can't talk myself into a scenario to explain it.

I welcome your thoughts and ideas. Thanks in advance.
 
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Old 11-25-16, 10:52 AM
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It sounds like you think it's one particular t-stat. Maybe a quick suggestion before getting into a bunch of questions would be to turn that one t-stat way up at least 10 deg. above room temp and see if it keeps things running longer. If it does then I would look at the stat. Does it due that with any of the others. Anyway it might be worth a try, If it does the same thing then the questions.
Hope this helps.
 
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Old 11-25-16, 11:13 AM
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Hard to tell if others exhibit same behavior, as I am not close enough to hear them click off and simultaneously hear the boiler stop firing (or not).

I can try your suggestion. I can also swap thermostats and see if it still happens. They are all the same model family - one touchscreen, two not. They all have the same settings.

Off for more experimenting...
 
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Old 11-25-16, 11:22 AM
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You do have the system type set to hydronic correct? I believe that is type 5.
 
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Old 11-25-16, 11:31 AM
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Yes, 5. I've set CPH (240) to 1, 2, and 3, with no change, but I'm not sure CPH is the issue.

I wonder if the Heat Manager is the culprit here. I can disable it for a bit.
 
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Old 11-26-16, 03:03 PM
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Tried a few things, but can't find a cause or pattern. I did find one 5-second sequence today that was initiated by TT, and ended by CFH. Can't wrap my head around that one.

As I mentioned in my initial post, I have three circulators on the 503, and the indirect DHW thermostat is connected to the Beckett. In this config, would TT always be the DHW, and ZR the circulators? I'm trying to get a better grip on the info in the history log on the Beckett.
 
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