Wifi thermostat shuts off during hot water priority

[Theodore]

Hi,
Per previous thread (https://terrylove.com/forums/index.php?threads/common-wire-question.78702/), I successfully added a common wire to my Argo AR861-211. But now there's a new peculiarity: when the hot water priority circulator to my indirect water heater (Superstor Ultra 40gal) is active, the power is cut off to the wifi thermostat (an ecobee3 lite). After the hot water production is satisfied, power is restored to the thermostat. If it's a cold morning and the hydronic heat was on, the boiler (Burnham MP0147) will shut down during the interim while power is restored to the thermostat. I understand why this happens, but wondering, is this just what we have to live with? Is there any way to power this differently with the controller I have?
Advice appreciated!
Thanks

 

[Jadnashua]

Without a full wiring diagram, it's not easy to say. Your symptom, though, implies that there may be two different 24vac transformers in your system, and you're tapping off part of both of them.

The red wire should be coming from the same source (transformer) as the common you ran. If you have a controller, it may have its own, separate 24vac source. In a typical system, it will always have power on it when measured to the C or common wire.

This might help https://smartthermostatguide.com/thermostat-c-wire-explained/

 

[Sponsor]

 

[Theodore]

Hi jadnashua
Below are wiring diagram and current image showing where I tapped the transformer (with the white wire) to make a common wire. Any advice is greatly appreciated. I'll also review that common wire reference you provided.

 

[Reach4]

Is that white wire soldered to the transformer your common wire to the thermostat?

 

[Theodore]

Yes, the white wire soldered to my transformer is how i created a common wire. That said, every time the hot water priority comes on, my new thermostat turns off.

 

[Jadnashua]

Many older boilers are oversized. You could try turning the priority switch off and see two things:
1. do you still get enough hot water?
2. does the thermostat stay on?

A priority circuit helps to ensure you feed your water heater at its maximum rate. That may not be necessary for your typical use patterns, and your boiler can handle both zones running at the same time without issues.

 

[Reach4]

Yes, the white wire soldered to my transformer is how i created a common wire. That said, every time the hot water priority comes on, my new thermostat turns off.

I was thinking that you might have been using place T3 on the diagram, but connecting right to the transformer would seem to make that not possible.

You could still flip the priority switch off as a test.

Where does the Rh wire connect?

 

[Dana]

Many older boilers are oversized. You could try turning the priority switch off and see two things:
1. do you still get enough hot water?
2. does the thermostat stay on?

A priority circuit helps to ensure you feed your water heater at its maximum rate. That may not be necessary for your typical use patterns, and your boiler can handle both zones running at the same time without issues.

Unless it's been down-fired with a smaller nozzle DOE output of the MPO147 is 129,000 BTU/hr which could theoretically heat my house down to about -150F or so outdoors. It's definitely oversized for any normal sized house with typical window (got glass?) and insulation values, and even oversized for the radiation in most homes. (Do you have 250' of fin tube baseboard or equivalent?)

The question is how oversized it is for the radiation when other zones are running, when the other zones would be sharing the output with the indirect. I suspect (but we don't really know until the radiation sizes for the other zones) that it'll work just fine to operate the system without priority zoning on the indirect.

 

[WorthFlorida]

Try it with the priority setting in the off mode. When it is active the only the priority zone will operate until its temperature is reached, then the Argo unit activates the other zone(s). Reach mentioned this in his post.

 

[hj]

You are describing a situation where you have connected to the 'hot' side of a switched device. When the switch is off you get a neutral flow through the device and it works. When the switch is on, the connection is to a "hot' wire, and as long as it is the same polarity as yours nothing will happen, and your device shuts off.

 

[Jadnashua]

Disconnect the T2 red wire, then measure from where you have tapped onto the transformer secondary and the T2 terminal (not the red wire). You should have 24vac. If you don't, measure from the other side of transformer secondary to the T2 terminal. If that now is 24vac, move the white wire to the other side of the transformer secondary (you should get 24vac from the two contacts of the secondary all of the time).

 

[Theodore]

Disconnect the T2 red wire, then measure from where you have tapped onto the transformer secondary and the T2 terminal (not the red wire). You should have 24vac. If you don't, measure from the other side of transformer secondary to the T2 terminal. If that now is 24vac, move the white wire to the other side of the transformer secondary (you should get 24vac from the two contacts of the secondary all of the time).

Did exactly as suggested: I get 24vac between the tapped transformer and the T2 terminal (not the red wire). So, sounds like I either live with the thermostat losing power every time the domestic hot water priority comes on, or shut off the domestic hot water priority and see if there are any complaints for early morning showers. Makes sense?

 

[Reach4]

Makes sense?

Not to me. The priority relay K3 shuts off power to the non-priority stuff when the priority calls for heat. I find the schematic potentially confusing. I marked up the schematic and added a black dot near T1 to indicate what I think the schematic is trying to indicate. The white wire I drew shows where I think your soldered-in wire should connect, but maybe I am off on that.

Where is the R terminal on the thermostat connected? The red wire that I drew for R is where I thought it should be connected (T1) , but I suspect R is connected to T3.

But I see the problem. Now how is the priority thing going to work? What keeps T4 from getting energized during priority? Not as simple as I first thought.

How about this? In this diagram, even tho you don't do cooling, you let the RC terminal get power to keep power to the thermostat, even when the priority water heating is on. Then by running the RH terminal to T3, the thermostat does not provide a circuit to T4 during priority. This idea makes some guesses about the thermostat, which may not be correct.

 

[Jadnashua]

I really hate it when the diagrams are sloppily done so you can't really tell when lines cross if there are connections there or not...it makes following the circuit much tougher. Good practice calls for either showing a connection dot to indicate there's electrical continuity there, or to use a semi-circular path of crossing wires to show there isn't a connection.

Essentially, you want your thermostat to get power from one side of the secondary, attached to the red wire and the other side of the transformer (the common) connected to the other. The thermostat should see 24vac when that's done at all times. Normally, the red wire is a constant voltage when measured to the common. When the thermostat is calling for heat, the internal switch closes and connects the red wire to the white wire. Back in the heating unit, that powers a relay, and the other side of the coil in the relay is attached to the common wire.

For what you're seeing, when the priority zone is activated, it would have to be disconnecting the red wire, which, should be directly connected to one side of the transformer. Doesn't make a lot of sense. unless there's circuitry that is not shown.

What's happening in the thermostat is when it is calling for heat, it connects T1 to T2 which causes a relay to close, activating things. The relay has the common on the other side of its coil, which completes the path so it can energize.

 

[Dana]

Seriously, with the massive BTU output of the MPO147, unless you have BEAUCOUP radiation on every other zone there is really no point to giving the indirect priority. That thing has 4x the burner output of a typical 50 gallon gas fired standalone.

While measuring the zone radiation would be a useful starting point for overall system optimization, testing whether taking the indirect off priority isn't difficult, and you'll know if it's a issue within a couple of days.

 

[Reach4]

There ya go... Slide the switch down to Priority Off, and the thermostat does not power off when the domestic water needs heating.