Thermostat C wiring issue

Question

I am having a two-wire system oil boiler with two-zone valves. I installed two Nest E and worked fine but it started to swing the valves due to the charging cycle. So I decided to run a new C wire from the C terminal of the transformer.

Here comes the problem. After I tracing the wires, looks like the wirings from the transformer are reversed. I drew the lines in the actual color of the wire.

So if I reversely connect (R W) wires to Nest E and connect new C wire from the C terminal of the transformer as below, all is well?

Or should I reconnect all zone valves too? I'd appreciate it if anyone can suggest a good solution for this.

Thank you!

What do the abbreviations mean? ST, 1F, C, TT? It seems like the three boxes in the middle should be relays but the symbol drawn is a transformer. — Greg Hill, Dec 10 '20 at 16:13

score 1 · Answer 1 · answered Dec 10 '20 at 18:42

You're right: the wiring colors as installed are "wrong" according to convention. The arrangement in the "after" drawing should satisfy the thermostats and operate the system correctly.

Because the wire colors are confusing it may be a good idea to re-mark them. You could get colored heat shrink tubing and use it to put a colored band on each conductor (or use colored tape). Shrink tubing is available in electrical supply and auto parts stores, among others.

Thank you so much! I will use those tube for the future. – neoengine Dec 10 '20 at 18:54 — neoengine, Dec 10 '20 at 18:54

Thermostat C wiring issue

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