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Taco SR503-4 Zone Switching Relay Control - wiring diagrams and installation instructions given here at InspectApedia along with contact information for TacoTACO Manuals, Parts Lists, Wiring Diagrams

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Taco Comfort Solutions Manuals Wiring Diagrams, Contact

Taco SR503-4 Switching Relay Wiring for a Cold Start Boiler application (no tankless coil) at InspectApedia.comTaco provides electronic controls for HVAC systems, thermostats, fan controls fuel mizer, zone controls, switching relays, and other equipment.

Illustration: an excerpt from Taco's wiring instructions for the Taco SR504-4 Switching Relay used for heating boilers - in this example where a tankless coil is not employed.

The Taco SR503-4 and similar controls permit setting up a priority zone that may be used, for example, to maintain a domestic hot water supply in an indirect water heater, as we expliain separately

at PRIORITY HEATING ZONE DESIGNS

Taco SR502 Two Zone Switching Relay Wiring Chart at InspectApedia.com

Above: wiring example for the Taco SR502 two-zone switching relay. See the SR502 instructions for important details and safety warnings. [Click to enlarge any image]

Taco SR503 Three Zone Switching Relay Wiring Chart at InspectApedia.com

Above: wiring example for the Taco SR503 three-zone switching relay. See the SR503 instructions for important details and safety warnings. [Click to enlarge any illustration]

Taco SR503-4 Zone Switching Relay Control - wiring diagrams and installation instructions given here at InspectApedia along with contact information for Taco

Shown above: Taco's SR503-4 Zone controller that can control up to 3 hydronic heating zones.

Valenmo V2313-A1S zone valve cited & discussed at InspectApedia.com

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Reader Comments, Questions & Answers About The Article Above

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Taco zone valve operating diagnosis & repair

Forgive me for the long intro, I want to make sure you have proper context. I have a gas-fired boiler with 3-zone hydronic heating system. 25 yr old boiler.

Taco zone valves (power heads are 1 yr old) and a Taco circulator (1 yr old).

Last year, I had a contractor come in since my system was not distributing heat very well to various areas of the house.

The contractor ended up draining the system and installed: a backflow preventor, a pressure reducing valve, and a new air removal (1 1/4" Honeywell) device.

My system did not have these previously. The air removal device was installed in series a few feet prior to the circulator pump.

The backflow preventor and PRV were installed in series from public water supply line and which ties into the system just below the circulator and prior to the boiler entrance. I think when this contractor left, there was a LOT of air in my system.

A few weeks ago, I installed two Nest thermostats. One on the main floor (zone 2) and one upstairs (zone 3).

For the upstairs thermostat, I actually had a dedicated AC tstat and a dedicated zone 3 tstat for heat and I combined those two functions into a single Nest. When I tested zone 3 on the Nest, the radiators lit up (pinged, got heat, etc.) but I only let run for 2-3 minutes and thought all was well.

Cutting to the chase, I think I have a number of problems and there is some bizarre behavior I'm trying to troubleshoot.

First, When my zone 2 tstat calls for heat, three of my zone 3 radiators get hot!

I have no check valves in my system.

These radiators only get a little hot though, they really don't produce much meaningful heat.

Second, when I have only zone 3 tstat call for heat, only the same 3 radiators get hot, and again, not very hot but they do heat up.

Third, my circulator pump started to make noise a few days ago.

Zone 1 will not heat AT ALL, zone 2 heats well but very slowly, zone 3 as described above.

All 3 zone valves have 24V and trigger the circulator properly both automatically and manually. Aric (Jan 11, 2015)

Reply:

Aric

It sounds as if there is a wiring error in the thermostats or zone valves or both, or shorted wires is causing un-wanted heat in zones not calling for it;

Other causes are a stuck-open check valve or zone valve on the other zones.

A zone that does not heat or heats too slowly may be air bound.

Aric

Do you know how I can check to see if a zone valve is fully or partially stuck open? I pulled the power cap off of zone 3 yesterday but I don't know where the lower piston should be sitting relative to the base plate.

I verified I could move it. I pulled off the functional zone 2 valve power cap as well to compare the zone 3 valve to it and they looked identical, height-wise.

How much distance do those piston actually depress? It seems the manual lever would only depress them a few mm at best?

Another test I ran was to physically lock down zone 2 and zone 3. I then manually opened zone 1 (which had no heat over the last day due to the tstat being shut off and the room was 54F) and there was zero flow to that entire zone.

That completely baffled me.

Thanks much for the advice/help!

Modeator Reply:

Aric
If you pull the motor head and look at the position of the valve stem or see if you can turn it that may help. But you'll need to refer to an un-damaged or working valve of the same brand and model for reference.

Before trying that see if you can move the valve with its manual operation level.

To be more specific we need to know the brand and model of zone valve.

Aric said:

Got it. It is a Taco zone valve and is stamped with 556 on the bottom side next to the directional flow arrow. Not sure if that is sufficient.

When you refer to "...see if you can turn it", what do you mean, specifically? The zone 2 valve I have I believe works entirely correctly.

Reply:

Aric the Taco 556 has a twist-off head that will expose the valve mechanical parts and it also has a manual bypass lever.

If you push the bypass lever and it's frozen then the valve is not operating.

(Jan 9, 2015) Aric said:
I flushed every zone/sub-zone of my system this morning and it behaves MUCH better.

An amazing amount of air had been trapped in one of the two circuits in zone 2.

There was some air in the other zone 2 circuit. Main floor and basement were good (no air). All radiators get hot now. I will double-check later whether or not the zone 2 valve still remains partially stuck open. Thanks for the help!

Reply:

Good news.

If air returns in any quantity in less than a year I think there is a leak somewhere.

Aric said:
Interesting. I'll keep an eye out for signs of any new air.

My zone 2 valve is definitely partially stuck open. When main floor or basement call for heat, hot water is being circulated on top floor (a bit, not full flow rate).

Any suggestions or good references for getting Taco 556 zone valves unstuck?

Reply:

Aric you might free a stuck zone valve temporarily by moving it manually between open and closed positions but in my experience that repair will not be reliable.

The zone valve needs to be replaced.

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