Thermostat not compatible

rudyrostum

Hello, I had a new Weil McClain E series boiler installed but my existing next thermostat is not compatible. Can someone please advise what smart thermostat is compatible with this boiler

pecmsg

Why is it not compatible?
make and model of t-stat?

HomerJSmith

Please--Don't tell @pecmsg it's a Nest. he'll go apoplectic.
A thermostat is just a switch. Just like every other thermostat. It's the charging circuit that gives everyone conniption fits. Other than Google spying on everyone, "How do you like them apples?"

KarlW

The problem is likely because your thermostat has no battery backup (pre-Google Nests like the one I started with did).

In most boiler installs the low water cutoff (including test mode) and pressure control both open when activated, cutting power to the thermostat.

Ecobees have the same problem. The key is to buy a thermostat with either a built-in battery charged by the 24v when active or one with an AA or AAA battery.

Jamie Hall

Watch out for the ones with the built in battery. Some of them -- and it would seem the various Nests are among these-- the battery is big enough to handle short periods of a call for heat, but not longer ones. In that case they need to have a common wire in addition to the control wire, and the common wire and R control wire need to be on an independently powered transformer. Doable, but a pain. That said, if it's a wi-fi thermostat, it's going to need that independent power. Battery powered ones simply don't have the battery capacity to handle the wi-fi.

dko

Jamie Hall said:

Watch out for the ones with the built in battery. Some of them -- and it would seem the various Nests are among these-- the battery is big enough to handle short periods of a call for heat, but not longer ones. In that case they need to have a common wire in addition to the control wire, and the common wire and R control wire need to be on an independently powered transformer. Doable, but a pain. That said, if it's a wi-fi thermostat, it's going to need that independent power. Battery powered ones simply don't have the battery capacity to handle the wi-fi.

Yes, the infamous honeywell lyric round smart thermostat. (no longer manufactured) https://www.honeywellhome.com/us/en/products/air/thermostats/wifi-thermostats/the-round-smart-thermostat-rch9310wf5003-u/
Sold well in the beginning. Advertised as a wifi thermostat with "optional 24vac." Had people replacing batteries weekly and soon into the garbage.

EBEBRATT-Ed

You can add a relay and a separate transformer to solve the Nest problem. The nest has battery that needs to be charged. Some boiler controls do not have an easy way to access the "C" wire needed to charge the battery and some of the boiler controls do not have a transformer large enough to power the Nest. See the attached wiring diagram.

KarlW

Jamie Hall said:

Battery powered ones simply don't have the battery capacity to handle the wi-fi.

My Netatmo thermostat optimized for boilers uses two or three AAA batteries to talk to a powered wifi relay that ties in the radiator valves. The initial batteries have lasted two seasons for me before being replaced.

The two AA batteries on the radiators themselves only last about one season, but they open and close a thermostatic valve.

 They really need to start Selling this in North America, I self-Imported from Europe

Jamie Hall

I imagine that for a short range, low speed application that yes, you could probably get away for a while with dry cells. It probably draws very little when it's off, and only activates the wi-fi for very short bursts. Be interesting to put a scope on it.

Not, however, what most wi-fi thermostats do...

EdTheHeaterMan

@rudyrostum, The reason your thermostat, that requires a C connection to operate, (most Smart Thermostats do) is because there must be a constant 24 volts from the transformer R (source) to the transformer C (return path) for the charging circuit.

If you are using a thermostat like that on your new boiler, there will be an error message whenever the Low Water Cut Off (LWCO) stops the burner from operating, because it breaks the R from the transformer before the thermostat R connection on the thermostat. This might be your Wiring Diagram here.

If you look at the RED thermostat on the left diagram, you can see that the Transformer R terminal goes to the LWCO, then from there it goes to the G terminal. Where the thermostat R terminal gets connected. Easier to follow on the Ladder Diagram on the right. When the LWCO opens to do its job, the power to the thermostat is interrupted and will present as an error on your smart thermostat.

There is an easy fix for that problem. The classic isolation relay trick. It requires a separate transformer and a relay, then the thermostat can be connected to that transformer and made to operate the relay coil. The relay contacts then operate the boiler as it would if it were a dumb (Switch only) thermostat that does not require a common terminal.

This is the normal industry standard to solve you problem with any smart thermostat, regardless of @pecmsg inability to accept them.
This might be the relay you can use: https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil?_br_psugg_q=rib+relay

This might be the transformer: https://www.supplyhouse.com/White-Rodgers-90-T40M1-Transformer-40VA-60-Hz-120V-Primary-24V-Secondary-Multi-Mount

If this is all greek to you, then your contractor can connect it for you, using the diagram in the attached file below