Adding Relay to interrupt TT?

CoHotelier

Morning - I'll try to make this as straightforward as possible - but will give as much info as I can.

We've got an Evergreen 220 (Weil-McLain) that will randomly Hardware fault most often during the changeover from Fin/Tube call to a DHW call.

Boiler is a Evergreen220
Fin/Tube Baseboard is connected via (4) Taco ZCV-406 to the boiler Input 2 tt. (22 zones iirc)
DHW is a HTP SSP-80 connected to the boiler priority 1 tt, pump is a 26-99 on spd1.
Boiler Pump is a 26-99 on spd 2.
Fin/Tube pump is a Magna3 set to auto adapt, and wired to the boiler additional heat contact TT (to the "start/stop" input of the Magna3).
In Place of a traditional Primary/Secondary Loop, the boiler is piped into a Boiler Buddy 18gal, with DHW loop connections made prior.

To satisfy very small zone calls, I have the Fin/Tube Call set to trigger the "additional heat demand" relay on the EVG220, with a delay of 10mins. This works WELL. On a heat call the boiler will go into standby, the Magna3 will spin, and if the existing warm water in the system incl the Boiler Buddy can satisfy the heat call within 10 minutes, the boiler doesn't fire. If the call isn't satisfied, the boiler fires and the Magna3 continues spinning.

To the problem. The hardware fault on the EVG220 will happen a handful of times per year - always at inopportune times because it requires a physical, manual reset. More often than not it happens during when the boiler receives a DHW call while running a baseboard call.

As a bandaid to this intermittent problem, I am considering putting the DHW call on a "additional heat demand" delay as well, of just 1min. That will ensure that the boiler fully spins down between the two calls - and ideally avoiding whatever is causing the hand-off errors leading to the Hardware Fault.

The issue is there is only ONE Additional Heat Demand contact relay in the WM menu/board - so if I enable this, then the Magna3 will spin up for every DHW call, and run until the DHW call is satisfied - in addition to the actual DHW 26-99 running.

The question, after all of this, is pretty simple. Can I put a spst relay in line with the Additional Heat Demand TT between the Boiler and the Magna3? I'd connect the normally closed and common relay terminals in series with either the red or white TT heading from the boiler to the Magna3, and the dry contact triggers would enter the same aquastat contacts as the DHW connection on the SSP-80 indirect. Can one Aquastat TT connection "feed" two devices? In this case, the boiler DHW (Zone1) contacts as well as the New relay Dry contacts?

This is the relay I had mind:https://supplyhouse.com/Functional-Devices-RIB01BDC-Enclosed-Dry-Contact-Input-Relay-20-Amp-SPDT-Class-2-120-VAC

The sum effect here wouId be the Indirects call for DHW would trigger the boiler to switch to DHW, start a 1min delay, and the relay I've just installed would open and break the "additional heat" tt being sent to the Magna 3. Once the DHW call was satisfied, the relay would go back to Normally Closed and the Magna3 TT circuit would be connected again.

EBEBRATT-Ed

Sounds like it will work fine. There are plenty of ways to do this.

Zman

I am not familiar with that boiler control, many have pump post purge options that will help with conditions like yours.

CoHotelier

Zman said:

I am not familiar with that boiler control, many have pump post purge options that will help with conditions like yours.

That's part of the problem. Sometimes the boiler just straight up ignores the pre-post purge settings. The other day I watched during a heat call. It got a domestic call and just straight up immediately started the DHW pump and went on its way. No prepurge for Priority 1 (dhw), no post purge of Priority 2(heat).

CoHotelier

EBEBRATT-Ed said:

Sounds like it will work fine. There are plenty of ways to do this.

Great, thank you!