Slant Fin GXHA-160 EDPZ with Google Nest thermostat.

Heating_Rookie

I recently bought my parents a new Google Nest thermostat. Unfortunately I am dealing with the need of a C connector. I opened up the boiler door and don't see the control board as in other photos. Looks to be a transformer with a bunch of wires. Can someone help me understand how to wire this up? Can I used the C connector on this type of boiler?

Steamhead

This is a steam boiler, correct?

Jamie Hall

Looks like it, @Steamhead . In which case, @Heating_Rookie , I'm sorry to say that the Google Nest is probably the worst possible choice of a thermostat you could inflict on your parents.

However, it can be made to work. First, you will be well served to use one of the outboard power supplies to try to power the thing. It might be possible to wire it into the boiler in some way. It might not. I believer Google peddles such things, for a handsome price.

Second, when and if you do get it running at least after a fashion, go into its various menus. You will want to disable all the "smart" features on it, and limit the setback to no more than once per day, and no more than 5 degrees Fahrenheit. All the occupancy features must be disabled. Set the cycle time, if you can find it, to 1 cycle per hour or, depending on the model, system type to "steam/gravity hot water".

Steamhead

Reposted from the Weil-McLain thread from earlier. This makes the thermostat circuit completely independent of the limit controls, so as long as the boiler power is on, the R terminal in the Nest will be kept energized. You will need a 3-wire cable between the boiler and the thermostat:


What I usually do with these is wire up an isolation relay to separate the thermostat power and control wiring from the boiler's stock wiring. This makes things a lot less complicated, and runs less chance of confusing someone who is looking at the boiler's wiring diagram. Any decent relay with a 24-volt coil will do, and you can mount it in the cabinet near the transformer.

If the thermostat also operates an A/C unit, it should have two "Red" terminals: R or RH is for heat, RC is for cooling. If there is a jumper between the two, remove it, otherwise the transformers in the two respective units may fight each other and burn out. Note that some thermostats expect the C wire to be associated with the A/C transformer. Check the instructions. If yours is like this, and it also controls an A/C unit, don't hook up the C terminal to the heating transformer.

Wire the "Normally Open" relay contacts to the boiler's thermostat leads. Use the following thermostat cable hookup to the thermostat: Red to R or RH (depending on which thermostat you will use), White to W, Green to C.

Now wire the Red wire in the thermostat cable to R on the transformer. Wire the White wire to one side of the relay coil. Run a Green wire from the other side of the relay coil to C on the transformer, and wire the Green wire in the thermostat cable to C as well.

This will provide a constant 24-volt feed to the thermostat electronics no matter what the boiler's limit controls are doing.

EBEBRATT-Ed

@Steamhead
I agree. A separate transformer and relay work with no fuss. I mount a 4" sq box with a cover mounted transformer and a RIB RIBU1C relay in one of the box kos

Ironman

“Looks like it, @Steamhead . In which case, @Heating_Rookie , I'm sorry to say that the Google Nest is probably the worst possible choice of a thermostat you could inflict on your parents.”

This ^^  ^^

People buy something based upon advertising gimmickry with the intention of saving energy not realizing how poorly it may interact with the type of system they have. A Nest should never be used with steam, hydronic or modulating equipment.

Buy a simple reliable thermostat that can be set to 1 cph, set it on one comfortable temperature and leave it there. That’s the best and most economical way to control a residential steam system.