Boiler / Control valve issue


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Old 02-12-14, 04:01 PM
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Boiler / Control valve issue

I have had an ongoing problem that I am stumped with. I have a Valiant gas fired, hot water radiator, cold boiler with 2 zones operated by one Taco 007 pump and two Taco 570 series zone valves. Both zone valves operate properly 95% of the time. Then there are the times when one calls for heat and the other does not but both run. When this happens I physically close a ball valve so I do not waste money. I have replaced one of the Taco heads because the small blob on the switch had broken off so the contact was not working. The other looks to be ok, blob is fine, wax solidifies when not calling for heat. I looked at the way Taco says 2 zones should be wired but mine looks nothing like this. Before I go tearing it apart and really muffing things up I want to get other opinions.

If you tell me how to post pics I have sketched out the wiring and have pics of the controls.

Thanks
Scott
 
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Old 02-12-14, 04:17 PM
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Yeah, something don't look right there Scott...

On the boiler, the R W G terminals, where are these terminals actually located? Are they on a control that has a transformer and a plug in relay?

Do you have the manual for the boiler? If so, can you photograph the wiring diagram from the manual and post it?

If not, tell us the full model of the boiler and I'll try to find it... or if you know of a place to find it on the net already, post the link to the manual... (save me time searching for it...)

By the way, searches will go better if you spell the boiler name correctly : VAILLANT
 
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Old 02-12-14, 05:36 PM
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Here are some additional pictures. Second pic is where the red/white/green come into the boiler. Looks to be a transformer.

Thanks
 
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Old 02-12-14, 07:51 PM
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As 'unconventional' as that wiring looks, it actually is CORRECT for this particular application.

I personally don't care for the fact that an internal boiler control transformer is being used to power the zone valves but with THIS particular boiler I think it's OK.

The reason I don't like this practice is because USUALLY when manufacturers use the R8285 control (which is what that transformer is a part of) the GAS VALVE is also powered by that same transformer. In this case with this particular boiler the gas valve is being powered by the OTHER Honeywell control so it's not really an issue.

So, that said, the wiring is correct.

You said:

there are the times when one calls for heat and the other does not but both run.
Can you clarify what you mean? I don't understand...

What do you mean "... both run ..."?

Do you mean that sometimes when one thermostat calls for heat that BOTH valves OPEN?
 
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Old 02-13-14, 03:53 AM
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Good news on the wiring.

An example of what happens is if porch thermostat calls for heat and the house one does not there are times when the house valve will be open and supply heat when the house thermostat does not call for heat. This does not happen all the time, only about 5-10% of the time.

Thanks again for the help.
Scott
 
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Old 02-13-14, 04:47 AM
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Trooper,
Isn't terminal 1 & 2 reversed? One should be hot from t-stat and 2 is ground. Three is end switch to boiler.
 
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Old 02-13-14, 07:01 AM
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An example of what happens is if porch thermostat calls for heat and the house one does not there are times when the house valve will be open and supply heat when the house thermostat does not call for heat. This does not happen all the time, only about 5-10% of the time.
That sounds like more of a mechanical 'sticking' issue rather than an electrical one.

Isn't terminal 1 & 2 reversed? One should be hot from t-stat and 2 is ground. Three is end switch to boiler.
That's what I thought at first but after closer examination I realized it's OK as-is, and in fact won't work any other way.

If I get a chance later this evening I will re-draw the wiring diagram and show why the wiring in this case is 'unconventional'. The fact that this system has the R8285 control and the installers are using the transformer on the control rather than an external one is the difference...
 
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Old 02-13-14, 12:55 PM
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What would you recommend about the mechanical sticking? Should I replace the innards of the valves?

So on the wiring was the installer incredibly smart or lucky?
 
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Old 02-13-14, 03:50 PM
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I guess the thing to do would be try and determine if it's the valve body itself or the power head that is causing the problem. Not sure how you would do that exactly.

Do you own a multimeter and know how to use it? If so, perhaps a start would be to wait for it to 'hang' and make some voltage measurements to make sure it's not the thermostat itself hanging... you can measure for 24VAC between terminals 1 & 2 when it hangs, if you have voltage there, it means the thermostat is telling it to hang.

If no voltage, then it still could be either the head or the body that's hangin'

I don't know that the innards are available as replacement parts... never looked actually...

So on the wiring was the installer incredibly smart or lucky?
My guess would be that he had some advice from the factory!

Here's how your system is wired:



24 VAC 'HOT' is wired to one terminal of each thermostat.

24 VAC 'COMMON' is wired to terminals 1 on both valves. Note that one side of the relay coil is ALSO wired internally to the R8285 control to the 24 VAC 'COMMON' terminal.

When thermostat 'makes', 24 VAC 'HOT' is applied to terminal 2 of the valve, completing that circuit, and the heat motor in the valve heats up and opens the valve.

When the valve opens, and the ENDSWITCH 'makes', it applies 24 VAC 'HOT' to terminal 'G' of the R8285 and completes the circuit to pull in the relay and fire the boiler.

Seems unconventional at first glance, but once one analyzes the circuit they will see that it makes perfect sense and is the only way this could be wired.
 
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Old 03-03-14, 07:33 AM
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Ok, here is an update. I replaced both thermostats, one was bad and one was just old non-programmable. I replaced both zone heads. For 2 weeks everything was fine and last night the house valve "hung" open. While it was running I checked the voltage on both valves. The porch valve that was calling for heat was 24v, the house valve that was not calling for heat was also 24v. Is it possible for the porch valve to be feeding the house valve at times?

I had checked both of these at different times over the past 2 weeks and everything was good. Voltage was proper at different times.

Thanks again.
 
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Old 03-03-14, 08:25 AM
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Ya know what? Your question caused me to go back and take a look at that diagram again and I have uncovered a defect in it's design...

Yes, it IS possible for EITHER valve to 'feed' the other, here's how:

Let's say at some point, BOTH thermostats call for heat and both valves open, both endswitches close.

Then, one thermostat satisfies... and it opens...

BUT, since BOTH ENDSWITCHES are CLOSED, the thermostat that did NOT open is going to 'backfeed' the other valve through the closed endswitch, and both valves will remain open until BOTH thermostats stop calling for heat.

Yep, that's the problem, let me look and see if there's a 'fix' for this.
 
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Old 03-03-14, 08:44 AM
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OK, I do have a fix, easy enough re-wiring of the zone valves.

I'll modify the drawing this evening and repost it.
 
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Old 03-03-14, 09:09 AM
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NJ, you will be my hero if you can figure this out. This has been going on for years.

Thanks
Scott
 
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Old 03-03-14, 10:34 AM
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NJ, when you reply later can you explain why this problem only happens at times?

Thanks
Scott
 
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Old 03-03-14, 12:49 PM
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Awww, garsh, now I'm gettin' all red in da face!

The reason it only happens at times is because it will only occur when both thermostats call for heat simultaneously, and then one thermostat satisfies while the other is still calling.

When this happens, both valves will remain energized until BOTH stop calling for heat.
 
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Old 03-03-14, 03:07 PM
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Here's your fix... simple rewiring, no more problem!

 
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Old 03-09-14, 10:33 AM
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Hey Scott, how'd it work out for ya?
 
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Old 03-10-14, 04:11 PM
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NJ, I have not responded because in the past it would seem good and then go wacky again. That said, I am very optimistic with this fix. It makes sense to me. So I am going to call it now, fixed!

Thanks again for your help and education.

Scott
 
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Old 03-10-14, 04:33 PM
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I'm confident that we found the problem... it was obvious to me once I 'saw' it...

You're welcome and good luck!
 
 

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