Navien boiler system with Taco sr503 relay

Old 12-15-22, 11:55 AM
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Navien boiler system with Taco sr503 relay

I have a Navien tankless water heater with a Taco SR503 3 zone switching relay.

The house has three zones:
- downstairs room/garage
- living room/kitchen
- upstairs bedrooms

Zone 1 is the downstairs garage. For some reason, the heat stays on in that room. The thermostat does not work. I've replaced it twice.

Yesterday the room was hot, while other two thermostats were activated. What does the green light mean for Zone 1?



Last edited by robrobinmtns; 12-15-22 at 11:56 AM. Reason: text missing
Old 12-15-22, 06:47 PM
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You have 3 pumps. Have you checked if Z1 pump is running when not calling for heat. When the Z1 light is on that stat is calling for heat. Can't tell but I believe you have cube relays in there which could be observed if the cover were removed. With 3 zones you could try switching cubes with one you know is working to see if that solves the problem.

Looking at the pic you sent it looks like just the power light is on and not Z1 but cannot be sure. If the Z1 light is not on you may have a bad Flocheck that allows water to flow constantly whenever any zone calls.

With cover off, and you still getting unwanted heat you can remove 1 stat wire from the control and see if pump stops. If pump stops you either have a bad stat or you may have a short in your stat wire.
Old 12-15-22, 09:31 PM
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Welcome to the forums.

Thread moved to the boiler forum.

Take the cover off the controller. In the picture it looks like only power is lit.
The light can spread from one LED to several zone indicators.
Old 12-17-22, 09:02 AM
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The green light only means power. When a zone is activated there will be a red light next to the zone. You probably don't have the cover all the way pushed on the control.
PJmax voted this post useful.

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