Rotating Vent Damper

CT

I installed a Viessmann ECD-S Boiler with a automatic vent damper controlled by a old Honeywell T87 thermostat, everything worked well until I installed a new Honeywell T8775 Digital round thermostat, now the vent damper goes round and round,(rotates 360 degrees steady). Any ideas

Ken_40

Double check

all the dip switch settings inside the 'stat.

We installed more than a few of these and have yet to find a "bad" one. You may be the first (;-o)?

Mitch_6

I have had this happen

on "some" other boilers with "some" clock thermostats. If there are not settings to change on the T stat you may need to use a relay to isolate it.

Mitch S.

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CT

When you put T87

thermostat back on, the old type with the mercury switch everything works fine, I think the new stat is not giving a steady call for heat

Mitch_6

Problem is

in the way the "Clock" thirmostat gets voltage through the vent damper circuit on the motor end switch.

I have only seen this happen on single zone boiler set ups.

When you have a relay in between the boiler and T stat there is no problem.

Mitch S.

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