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Old 06-18-2020, 03:42 PM   #1
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Issues with boiler short cycling when AC is on

Hi there - I am new to the forum and I apologize if my question is dumb. I am handy, but not an expert on HVAC systems so was hoping someone who is could give me some advice.

I have the setup as follows which was installed before I bought the house. Two zones, two thermosats, two hydronic air handlers (Comfort-Aire AHG24-0A) and one shared high efficiency Utica boiler connected via a valve control panel (Taco ZVC403).

In trying to improve efficiency, I tried installing an ecobee with voice. Because I only had 4 wires, I installed the PEK. The system worked great all winter, zero issues and I love it. Then, I needed to turn on AC...

I happened to be in the utility room and when the AC was running I could see the taco orange light for zone 1 would periodically start coming on intermittently until eventually zone 1 valve would close and the boiler would be initiated. By the time the boiler started, the taco panel lights would go off. This would then happen again a few minutes later as long as the AC was running.

Thinking it was the PEK, I removed it and ran a C wire to the air handler. The same issue persisted. I removed the ecobee entirely and backed out the C wire and installed the original relay based thermostat. Guess what - the taco panel is still intermittently calling the boiuler for heat via zone 1 when the AC in zone 1 is running.

Right now, I have disconnected the zone 1 connections to the Taco panel to stop the boiler being repeatedly cycled. My question(s) is:
  • Has the Ecobee damaged the air handler of Taco panel to cause this?
  • Does the taco panel need to be connected via the air handlers two white wires of can it be connected directly to the thermostat?
  • What could cause the panel to do this, even with a regular relay thermostat?

It is quite possible this behavior has always happened and I just didn't know about it. The contractor on this house made many bad choices.

Any help truly appreciated - sorry for the long email!
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Old 06-18-2020, 03:52 PM   #2
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Re: Issues with boiler short cycling when AC is on

I'm unfamiliar with the type of setup/controls your have, but would try an isolating relay on the W signal/at the panel.

The ecobee doesn't use mechanical relays so there can be some current leakage sensitive electronics pick up
I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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