I made a run at this problem way back in quarantine times, but eventually put the thermostats on the shelf and moved on from this as yet unsolved problem.
Love to get some advice! Ready? Okay.
We have a gas-fired boiler. This boiler feeds 3 zones with hot water baseboard heat. Each zone is controlled by a valve (plumber calls it a "power head.) How this works is - when a thermostat calls for heat, the valve opens to let hot water flow, and the valve also trips the boiler circulator pump to switch on. Works great with ordinary two-wire thermostats, one per zone.
I ran a brand new 5-conductor wire to the thermostat through some walls. All these connections are fresh and new.
First, I connected the boiler’s 75ma 24vac transformer directly to the Wyze thermostat. Transformer directly to Rc and to C. When I stop here, the thermostat works beautifully. Steady stable power, firmware upgraded, displays temperature. It’s happy humming along on the wall downstairs while the furnace is busy running. So clearly there’s plenty of power from the transformer to open and close valves and run the boiler while my Wyze thermostat is running. But it is not yet controlling the furnace.
Next, I connected the thermostat to the zone valve, Zone valve is connected to Rh and W1. I simply copied the wiring from valve to our old, existing thermostat - and redirected those wires to the Wyze thermostat instead.
Now, when I switch furnace back on, the Wyze thermostat repeatedly shuts down and reboots every few seconds.
It’s got to be something about the Rh-W1 connection to the zone valve that is doing this. Is there logic in the Wyze thermostat that defeats the steady dedicated power I’m already sending to it from from the transformer over Rc and C? Do I need to play with the app some more?
Penny for your thoughts!
Do you have a zone controller box? Everything seems to me that there is too much draw on the 24v system causing the T-stat to reset.
No. And I upgraded the thermostat from its original 20va to a new 75va. Doing the math, my 4 existing power heads should leave plenty of juice available for the Wyze thermostat.
I mean it could be this, but. Just running the tstat while furnace is operating works fine. Maybe I’m missing a programming thing?
My gut is the surge on opening the zone valve is throwing the power off just enough to freak out the T-stat. Holding a valve open might also cause noise that is freaking out t-stat. I had a similar problem a couple of decades ago with a tricked out pinewood derby track and magnetic release gates causing the digital timing system to reset.
I’m trying to think of a test for my hunch. But without relays /controller box that might be hard especially with AC power.
Do you have a 24vac coil relay that can trip on the thermostat W1 and close the coil on the zone value with a different transformer ?
Hm. Wouldn’t know about a relay. What I do have is the old 20 transformer I suppose could also hook up to just use as a power supply. That kind of scares me a bit having two transformers touching a single thermostat.
I can’t be the only person seeing this problem.
Using two transformers in the same circuit would not be a valid test. We are ultimately trying to isolate rf noise in an ac circuit. Hard to do without a relay.
Install a 24v isolation relay. Your aquastat (power head) is probably expecting tt and th dry contacts, and the wyze is trying to dump 24v into it. also, It’s unlikely that the Rc of the power transformer and the th (R) terminals are at the same potential, so the wyze might be experiencing spikes of up to 200v on its circuits.
OK, thanks for laying all this out. I may try this.
In fact, googling this relay idea, it looks like many OTHER smart thermostats actually talk about this in their instructions. There’s a nice video that lays it out very simply.
Installing smart thermostat with boiler using a relay - YouTube
Why does Wyze ignore such a common situation? Too bad really.
nice. So shouldn’t tap the existing transformer for both the thermostat and the valves? that’s my current setup.
depends on how it was wired with your old system- do your valves expect 24v or are they TH and TT (dry) contacts ?
From each one, a pair of yellow wires connect to the two-wire thermostat, and a pair of black wires are attached down at the boiler’s control panel.
Something like this then? they have an internal power supply and dry contacts.
if the previous thermostat only had 2 wires and they both went directly to the aquastat, then you have dry contacts, and it is not expecting to get 24v from an external power supply dumped into it.
Pictures of your setup would help me diagnose the exact issue greatly.