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OK. I see a problem. you have the C from the thermostat going to the same place as one of the R or W on the thermostat, That is where you have the Red X.

Just changing the C to the other side of the zone valve may or may not solve the problem. Here is an example of how it will not work.

In this picture, the R from the transformer goes to one of the yellow wires or to the TR on the zone valve. The Other yellow wire from the zone valve or the TH goes to the R on the NEST. The C from the NEST goes to the R on the transformer and the W from the NEST goes to the C on the transformer.

This is an example of how it will work:

In this picture you can clearly see that the R from the transformer goes to the R on the NEST. The W from the NEST goes to the Yellow wire or the TH on the zone valve. The other Yellow wire or the TR on the zone valve goes to the C on the transformer. And the C from the NEST also goes to the C on the transformer.

BUT….

Don't just change the wires on the one zone valve if you need to. All the Zone valves MUST be wired the same. To be clear, If you need to swap a wire from W to R on one zone to make it work, then you must change W to R on every other zone the same way. Otherwise you may let the factory installed smoke out of the transformer. That can get expensive and it doesn't smell very nice either.

You can always get one of these smoke keepers from the auto parts store. You want the 3 amp variety.

PS… I don't really sell these. They are cheaper at the auto parts store