Taco SR503-EXP Relay problem

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  #1  
Old 11-04-18, 04:18 PM
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Taco SR503-EXP Relay problem

We have a two-zone hot water heating system in the house with the boiler and radiators. Nothing else is connected to it. We've had it for over 10 years, and it had worked well. This year, our main part of the house (zone 1) is overheating. Heating usually stops when the temperature reaches the one set on the thermostat, but often early in the morning, hot water runs up the pipes and radiators when the temperature is already much higher than the one set up on the thermostat. It looks like this happens when the lower part of the house (zone 2) is getting heated. For some reason, the relay is not working properly. I suspect a fuse in Taco SR503-EXP relay might have gone off. Could this be a correct assumption, and if not, what else could have happened? Thank you all!
 
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  #2  
Old 11-04-18, 05:06 PM
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Welcome to the forums.

We're probably going to need pictures...... How-to-insert-pictures

Do you have zone valves or multiple pumps ?
If zone valves..... one might be staying open when it shouldn't be.
If circulator pumps..... you may have a problem/stuck flow check valve.
 
  #3  
Old 11-05-18, 10:32 AM
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Thank you! Will add pictures today.
 
  #4  
Old 11-05-18, 09:55 PM
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Posting pictures my wife took today (I am traveling). Please let me know whether this is sufficient. Thank you!
 
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  #5  
Old 11-06-18, 10:19 PM
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This is all we have. Looks like we have three circulator pumps. How do we test it for a problem? Or do we have to call a technician? Thanks!
 
  #6  
Old 11-06-18, 10:55 PM
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It looks like all three zones are connected. I see what looks like two floor radiant loops and manifolds.
Do you have a domestic hot water storage tank connected there ?

On the side of the Taco unit is three red lights showing which zones are active.
Do the lights go out for the zones that shouldn't be heating ?

When you have circulator pumps you need to have check valves in the line to keep the water from flowing in a zone that is not calling for heat. You have three pumps which means there should be three check valves. I don't see any. It is possible that those pumps have the check valve in them and one is not closing as it should.
Can you post the model number off one of those pumps.
 
  #7  
Old 11-07-18, 12:32 AM
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Thanks for replying so quickly.

1. We do not have storage tank connected. We have a tankless water heater which is not connected to the heating system.
2. The lights are red on both zones (actually, three for some reason, in addition to green main light, even though we only have two zones), even when zone 1 should not be heating.
3. The circulator pumps are Grundfos UPS15-58FC. The description says "with integral check valve".

Thanks!
 

Last edited by vadimts65; 11-07-18 at 01:57 AM.
  #8  
Old 11-07-18, 01:12 AM
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I see three circulators and all the red lights are on. What is the third one for ?
 
  #9  
Old 11-07-18, 01:56 AM
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I don't know... How would I check?
 
  #10  
Old 11-07-18, 06:45 AM
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When you turn the Tstat down below set point do those lights on the control go off?
Geo
 
  #11  
Old 11-07-18, 07:15 AM
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Thanks for the question. If zone 2 thermostat setting requires heating of zone 2, the red light for zone 1 stays red even if the temperature in zone 1 part of the house is already above the one set on zone 1 thermostat. Does this help?
 
  #12  
Old 11-07-18, 10:32 AM
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Here is what we found.

When the boiler is not working (the temperature in each zone is above the one set on the corresponding thermostat), the green light and ALL THREE red lights on the Taco relay are still on.

It was scorching hot in the main part of the house during the night even thought the temperature was set to 67 degrees. We are now waiting for the radiators and pipes to cool down. We will then increase the temperature setting on the lower zone thermostat to start heating the lower part of the house to observe whether this truly causes the main part of the house, which is on a different zone, to start heating as well.
 
  #13  
Old 11-07-18, 10:44 AM
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V,
With the stat on the hot zone satisfied and if the light is still on at the relay take a screw driver and put the metal tip on the pump canister and the other end to your ear and see if the pump is running even though the stat is not calling.

You may have a relay issue and not a flow problem.

Just a thought, hope it helps a little.
 
  #14  
Old 11-07-18, 10:49 AM
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In order to confirm whether it's a control or thermostat wiring problem..... you'll need to remove the thermostat wiring from the controller to see if it stays active.

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  #15  
Old 11-07-18, 11:21 AM
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I forgot to mention that we tested the thermostat in the main (problematic) part of the house. When the boiler was not running, I raised the temperature setting on the thermostat. The boiler started working immediately. So, looks like the thermostat is wired properly.
 
  #16  
Old 11-07-18, 12:16 PM
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Thanks! We will try to listen to the pump. Do I understand this correctly: if we hear the pump working when the boiler is not running, something is wrong with the pump? Otherwise, it is more likely to be a relay problem, correct?
 
  #17  
Old 11-07-18, 02:19 PM
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If the pump is running when the stat is satisfied your problem would most likely be in the relay.
Your pump should only run on a call for heat.
 
  #18  
Old 11-07-18, 03:32 PM
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Thanks. Will check later today.
 
  #19  
Old 11-07-18, 07:05 PM
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The pump is running when the thermostat is satisfied, which means something is wrong with the relay. Should we assume that fuse(s) went off?
 
  #20  
Old 11-07-18, 07:34 PM
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Not likely a fuse problem.
Geo
 
  #21  
Old 11-07-18, 07:37 PM
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Look at post #14 and see what PJ circled. One of those pair of stat wires goes to your stat on the overheated zone and below is the corresponding pump.

If you remove 1 stat wire to the bad zone see if the pump stops. That stat wire is 24V so it's not a problem if you don't shut the power off first.

If that does nothing then pull the square relay cube and see if that kills the pump. It may be stuck. If it shuts the pump off then try another cube from a working zone and see if that fixes the problem. If so then you need to replace that cube.

Those pump wires on the bottom are 120V so remember to kill the power if you're going to remove any of those wires.
 
  #22  
Old 11-08-18, 01:47 AM
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Thank you PJ, Spott, Geo!

We will check the things you recommended and post back here.
 
  #23  
Old 11-08-18, 02:10 AM
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Should I buy 24V or 120V replacement relay cube?
 
  #24  
Old 11-08-18, 05:12 AM
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Hi, I would be sure those relays are removable .
Geo
 
  #25  
Old 11-08-18, 12:49 PM
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Do you know whether different relays control the boiler and the pump? We tested and found that when the boiler is not heating any part of the house, raising the temperature setting on the thermostat in the main, problematic part of the house triggers the boiler to start working. This implies that the relay talking to the boiler is working fine. However, the pump connected to the zone heating the main part of the house is working even when the boiler is not, likely implying that the relay controlling the pump is not working properly. However, if both the boiler and the pump are controlled by the same relay, the problem must be with the pump because the relay does work properly with the boiler. Thanks!
 
  #26  
Old 11-08-18, 01:13 PM
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Have you tried removing the Tstat wire from the control? as Pete mentioned, its odd that all 3 zone lights are on if only one zone is calling.
Geo
 
  #27  
Old 11-08-18, 02:04 PM
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To G's point pull gently just in case but I believe they are replaceable.

When you remove it, it will have specs on the side. Just duplicate what is there.

[url]https://www.supplyhouse.com In the search box type Taco Relay ice cubes.
 
  #28  
Old 11-08-18, 03:21 PM
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I'm not sure if your unit is exactly like the one I posted. There are many variations and hard to keep up with. If you only have three relays inside yours..... then they are two pole relays and each relay controls the boiler and its respective circulator.

It's extremely rare for one of those relays to get stuck on. Be sure all the zone lights are out first. If one stays lit and shouldn't be.... that's a problem.
 
  #29  
Old 11-08-18, 03:25 PM
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Spott: I seem to be confused. Should I pull the wires, as circled on the photo above, or should I pull the ice cube(s)? Or both? Thanks!
 
  #30  
Old 11-08-18, 03:28 PM
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You should pull the wires off and see if all the zone lights go off. That's what should happen.
Be sure to mark which set of wires was on which terminals.
 
  #31  
Old 11-08-18, 03:45 PM
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As PJ said, pull the stat wire first. If the pump stops then that will tell you that your problem is between the stat and the control. Since you already pulled your stat and the pump continued to run it could possibly be a bad stat wire.

There is no need to pull all the wires. Just the one for the bad zone.

If you pull the wire and the pump continues to run then pull the cube and the pump should stop.

If it does try one of the other working cubes to see if that solves the problem. If so, then you can replace the cube.
 
  #32  
Old 11-08-18, 04:25 PM
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Thank you all! Will report this evening .
 
  #33  
Old 11-09-18, 11:11 PM
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Here are the photos of the inside of the box. Turned out zones 1 and 2 are wired together for some reason. These are wired to the thermostat in the main, problematic part of the house. Zone 3 serves the lower part. I am away this week. Before my wife turned the entire system off in the electric panel, all three red lights were on but the furnace was not working - it was already warm everywhere. After she turned it off and then on, the lights went off. When she raised the setting on our thermostat, red lights for zones 1 and 2 went on and the boiler started to work, as expected. When she lowered the temperature, lights went off and the boiler stopped, as it should do. She could not test zone 3 thermostat - people downstairs already went to sleep. We'll explore and report tomorrow morning. If resetting the whole setting in the panel did not solve the problem, what could be the reason why when zone 3 thermostat calls the boiler to start working, zones 1 and 2 also start working? Which relay could be at fault? And why are there four relays, not three?
 
  #34  
Old 11-09-18, 11:19 PM
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Here are the photos of the box.

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Last edited by PJmax; 11-11-18 at 01:32 PM. Reason: reoriented, resized, enhanced pics
  #35  
Old 11-11-18, 06:24 PM
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The red lights are off now when the boiler is not working. It seems simply turning the switch on the panel off and then on solved the problem. Very strange. Any ideas why this could have happened? I will report here if the problem reappears. Thank you all for your help!
 
  #36  
Old 11-12-18, 02:02 PM
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You may have had a relay that got stuck and by shutting the power off & on is how you reset the control.

Just a thought. Thanks for the update.
 
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