Nest thermostat/2 zone issue.

Crcote320

Hello all,

I’m hoping someone can help me. I have a heat only, oil furnace with baseboard heat. Last year I installed a nest thermostat, but my thermostat only had 2 wires. Everything was working great until I paid a contractor to add a second heat zone in my basement, which also now has a nest thermostat. The contractor used a 3 wire so there is a C wire for my downstairs nest. Both thermostats work fine independently. My issue is that my heat upstairs (the original zone) won’t work if the heat downstairs is on. If it is already on, it will shut off when the downstairs zone kicks on and if the downstairs zone is on, the upstairs zone just won’t turn on at all. It should be noted that the upstairs nest thermostat never loses power and it appears to be working, it just won’t kick the heat on while the downstairs zone is active.

I’m assuming this is some type of power issue/wiring issue where the downstairs zone is taking control. My question is if it’s possible to make it so that both zones can work at the same time if there is no c wire in my upstairs or am I basically stuck keeping it the way it is? Also, running new wire really isn’t an option bc my basement is partially finished and it would cause a lot of work to run new wire to my upstairs thermostat. Any insight or help would be greatly appreciated. Please keep in mind I have very little knowledge when it comes to heating systems, but I do have some basic knowledge/skills with wiring. Thank you!

HVACNUT

It seems like a wiring issue.
Can you post some pics of the boiler, controls, and wiring?

Crcote320

Crcote320

So the only thing that’s really cluttered is the aqua smart box. If need be, I can get some better pics of inside that box. The first thermostat pic is the downstairs thermostat which seems to be considered the master thermostat now since it has preference over the other one. The second thermostat pic is my upstairs thermostat which has only 2 wires.

The first thermostat is wired into that aquasmart box which has wires going to the upstairs taco circulator and then wires to the taco zone box. The taco zone box has wires going to the downstairs circulator and then to the downstairs thermostat. I can get better pics of how the the circulators are tied together in the aqua smart box if you need them.

I would really appreciate the help!!

HVACNUT

The SR501 needs to be wired per the diagram "Alternative wiring (tankless coil).
And tell the contractor a green wire on a line voltage circuit is for a Ground only! Somebody is gonna get zapped. Use Blue.

STEVEusaPA

Why is the green wire on RC in the Nest

Crcote320

I appreciate both comments! I will google that diagram and do my best. Do either of you think my issue is being caused by the fact that there is no common wire for the upstairs thermostat? Some sort of power stealing issue?? I am going to find that diagram and try to rewrite it... before I do that, do either of you have any advice before it do or possibly do this? I know everyone is busy so I appreciate it!!

Jamie Hall

Two comments... first, agreed on the green wire. Although a smart electrician will check all the wires for voltage for sticking fingers or tools in, green is always ground. Always. Not common. Second, the Nest wired with three wires is nice, but... you have no common connection there on either the heating or cooling side. Not quite sure what will get messed up with the rest of the show wired that way -- I'd have to see the whole wiring schematic, and it depends a lot on what the other end of that green wire goes to -- but that bit of it at least is simply not right.

Crcote320

Jamie, the other end of the green wire of that second nest is wired to the 24v com connection in the taco zone box. Should I switch that to the C connection in the thermostat?

Crcote320

From what I can tell so far the sr501 is wired properly. What is the ZC and ZR??

Jamie Hall

If that green wire on the thermostat is the other end of the green wire in the photo you posted of the switching relay earlier, then … it is the common wire and should go to the common terminal on the heating side of the thermostat.

ZC and ZR are the common and power open contacts for a zone valve.

HVACNUT

The relay wiring is correct.
I'm not real familiar with the Beckett Aquasmart but maybe it needs reprogramming to accept and additional zone.

CTOilHeat

Regarding the zoning issue, the aquasmart may be set on domestic hot water priority if the relay is wired to ZR. This is to provide HW production before space heating.

The aquasmart doesn't know what you are using it for and is prioritzing the "ZR" zone before it allows the circulator contact on your other zone to energize.

So it MAY be just a setting on the aquasmart to change. (Page 29)

https://www.beckettcorp.com/wp-content/uploads/2015/01/AquaSmart-7600-Burner-Control-Manual.pdf

Crcote320

CTOilHeat,

THANK YOU SO MUCH!!! I looked up the setting you mentioned and saw that DHWP setting was set to on ZR. I turned it off and now both zones work and at the same time! Thank you so much for you help everyone!!