Thermostat rapid cycling?

Camperch

Jamie, I started with CT87K

Camperch

OK, were all tired of this trivial problem, think we beat it to death, I want to thank everyone for your patience and input. To answer the question the load of the zone valve does go through the thermostat it is not isolated at the control board. Also system low voltage is 26V and when loaded down with both zones calling it goes to 22.5V. I am going to keep the Honeywell CT87K on line in the 2nd floor and monitor it. New LUX stat arrived today, but I want to see if the yo-yo acts up. For sure, stay away from the Mechanical Honeywell in these applications.
Thanks to all, I'm sure you have plenty more post to address on this site.
Matt

109A_5

hot_rod said:

Doesn't the thermostat just see the relay in the Taco box, not the actual zone valve load? I thought the relay isolated the load from the stat?

This sure sounds like more than a T-stat issue.

@hot_rod In the TACO 3 zone controller (ZVC403) I don't think there are any zone relays like in the 120 Volt units. So the thermostat sees the Zone Valve loads in this case.

@Camperch, I believe the intended current path is what I marked in Red, any other path near the magnet may just be coincidental by the design. I believe the current does not go through the bi-metal (curly-Q) that senses the temperature. Depending on the setting it does go through the resistance wire (probably an alloy and not bi-metal) for the Heat anticipator. Glad you have it all working better now.

Camperch

109A_5 -----Yes, I agree, thanks