Taco 503 - power flashing green

dmel

Everything was working fine, all of a sudden when my nest is calling for heat, instead of the zone turning on, the power LED starts flashing. It is a single flash every approximately five seconds. 

I can't find any manual that explains what this flashing power LED means. Any suggestions?

HVACNUT

SR503? When the Nest is not calling, the green light is steady on as it should be?
How is the Nest wired? Is it using the transformer in the 503? What are the other 2 zones controlling? 

EdTheHeaterMan

Is is possible that the nest is causing a dead short on the transformer and immediately reseting every 5 seconds?

Take a picture of the way you wired the Nest and the Taco 503

Derheatmeister

New install ? Or has this Nest to Taco install been working for a while ? What happens when the Nest you disconnect the Nest from the Taco and just jumper the therminals to call for heat?

dmel

Derheatmeister said:

New install ? Or has this Nest to Taco install been working for a while ? What happens when the Nest you disconnect the Nest from the Taco and just jumper the therminals to call for heat?

It's not a new install. We're having work done in the adjacent room so I thought maybe they pierced the wire with a screw or something but no. 

When not calling for heat, there is a solid green power LED. When I remove the nest and just touch red to white wires, the green power light dims on the SR503. Zone led never comes on. 

EdTheHeaterMan

dmel said:

It's not a new install. We're having work done in the adjacent room so I thought maybe they pierced the wire with a screw or something but no. 

When not calling for heat, there is a solid green power LED. When I remove the nest and just touch red to white wires, the green power light dims on the SR503. Zone led never comes on. 

The next test is at the 503. Remove the thermostat wires from the 503 and touch a jumper on the R and W wire terminals directly at the 503. See if removing the wire gets the same result or a different result.

dmel

EdTheHeaterMan said:

It's not a new install. We're having work done in the adjacent room so I thought maybe they pierced the wire with a screw or something but no. 

When not calling for heat, there is a solid green power LED. When I remove the nest and just touch red to white wires, the green power light dims on the SR503. Zone led never comes on. 

The next test is at the 503. Remove the thermostat wires from the 503 and touch a jumper on the R and W wire terminals directly at the 503. See if removing the wire gets the same result or a different result.

Jumping the terminals directly on the 503 works. Sigh. Thanks for holding my hand through this. I'm embarrassed I didn't think to triage this way on my own. 

So before I run new 18/3 across the whole house, any idea what may be the issue that's causing this dim power led with no actual call for heat? 

EdTheHeaterMan

There is a nail or screw or a pinched wire in the thermostat wire somewhere. the W wire and the C wire are connecting somewhere. When R and W are connected at the thermostat during a call for heat, then you get a dead short from R to C (thru W). The NEST is smart enough to disengage the call for heat if that happens and then try again.

HVACNUT

Can you tell or show us how the Nest is wired? R,W,C on the Nest connect to ?

EdTheHeaterMan

HVACNUT said:

Can you tell or show us how the Nest is wired? R,W,C on the Nest connect to ?

This is top secret stuff. If he shows you , he will have to kill you!

SteveSan

Does the sr503 have a metal or plastic cover? How many Nest are you connecting to the sr control? Do you have a com coming from the Nest to the Taco sr control?

EdTheHeaterMan

You got to use your head in the big stuff!

dmel

All fixed! Thanks for the tips. I had inspected the 18/3 and not seen any obvious mail punctures but Ed's tip about a pinched wire had me look further. Sure enough, I stripped the shearing and there was a specific point where the white and red were stripped inside the cable, causing the short. All running well now, and we have heat

Thank you all!

HVACNUT

dmel said:

All fixed! Thanks for the tips. I had inspected the 18/3 and not seen any obvious mail punctures but Ed's tip about a pinched wire had me look further. Sure enough, I stripped the shearing and there was a specific point where the white and red were stripped inside the cable, causing the short. All running well now, and we have heat

Thank you all!

Glad you found something,  but if the Red wire is 24v to R on the Nest, and the White wire is from W on the Nest, then how would that effect the green light on the 503? What it should've done was sporadically power that zone and the corresponding RED light for that zone, no?
Unless the White wire is being used as the Common and the remaining wire is W. If only there was a way you could show us.
Or maybe the Nest doesn't like 24v going backwards into W. Not without asking nicely first anyway.