installed 3250-plus; now it's burning up thermostats, help please.

First off I'm not a pro at this stuff but am pretty handy and thought I could handle this job...but apparently not

I've got:
crown boiler
beckette oil burner
argo azv 246p zone valve control
3 zones plus a water heater zone- Taco valves
replaced a L8148 with a 3250-plus (bought used for 2 weeks)

My problem seems to be that after I replaced my aquastat with the 3250-plus when I get a call from one of the house zones it'll burn up a thermostat.(send voltage through the red white wires?) I already lost a cheap one that I didn't care about and when trying to diagnose I was getting that electrical burning smell from another (then quickly disconnected). I wired up the 3250-plus with all the same wiring from the aquastat and did not touch the wiring of the zone control until I was try to diagnose.

Like I said some of this stuff I don't know. but I'm questioning weather I should be getting 30v coming from the TT of the 3250-plus. doesn't seem right to me that it's sending voltage the zone control when the control already has ~24v.

any thoughts? what else should I test?

Thanks for any help,
RAY

 

Ok, maybe this'll help. with or without the 3250 connected to the zone control I'm getting 27v at the TT on the zone control. essentially putting 27v to the thermostat @ The W and RH. is this correct?

 

Yes, sort of.

The Rh is of course the 24 VAC hot side, the w is coupled to the com of the transformer thru the electronics. The impedance of your meter is so high that it does not disctinguish the fact that the electronics pull it low. If you jumper across Rh and W the zone should turn on.
If, when you jumper between Rh and W, the LEDs dim or the fuse blown then you can suspect the zone control board.
The problem might be the actual zone valve is pulling too much current for the stat.
I would be checking the zone valve for that zone with an ammeter.

Oh, BTW. 27 to 30 volts ac is not unheard of for 24vac control transformers

 

Especially if you are close to the hydro plant and your nominal AC line is at the high end of 'normal'.

My typical AC line here, where I'm only about a mile from the substation, is about 127 VAC.

More voltage on the primary of a transformer will of course give a higher voltage on the secondary.

What is your nominal AC line reading?

 

I'm unsure how to check the amperage, but I did notice that the taco valve for the zone that caused my thermostat to have that electrical burning smell was not testing like the rest. upon further testing and jumping the TT the valve was getting the 25ish voltage on 1 and 2 but it was not pushing out and activating the end switch. could this valve acting in such a way cause my thermostat to overload? these thermostats are not cheap and I'm a little nervous to turn on my other two zones. I guess what I'm asking to be sure is, is it possible there's a bigger problem causing my valve to blow and thermostat to overload?

thanks for the help!

 

You need to ensure the load imposed by the zone valve is less than what the thermostat is capable of providing.
It is quite possible that the zone valve is failing and there is certainly a possiblity that it is overloading the stats.
The only way to prove what is going is to measure the current draw on the zone valve. Since it doesn't seem to be making the end switch this would indicate a problem and the need for replacement.

 

youtube taught me how to read amperage. makes a lot of sense surprised I didn't know it!

So the suspect valve head, the one that potentially burnt my stat, was getting the 27v, but no amps. remember it's not pushing out and triggering the end switch. I assuming this one is now shot.

the other three valve heads were getting the 27v and 1.18-1.22 amps

the manual for my thermostats says no more then 1 amp or it may cause damage.

the thing is I've had these thermostats hooked up for 1.5 heating seasons. so where they always getting more amps than they're supposed to or is the control going? does anyone think the extra amperage is a problem?

Thanks again!
RAY

 

really depends on the stat.
The older more mechanical ones could probably take a bit more variance in the load, ie handle more current.
If a newer electronic stat has relays then they might be ok with some overload, but if it's a current source or sink transistor output overloading that will cause damage fast.

 

One of the purposes of a zone control panel is to isolate the load of the zone valve from the thermostat. I see a relay on the "priority" zone but not on the other zones so it might be that the other zones use a transistorized (more likely a triac) switch to control the zone valve.

In my opinion, either you have the panel incorrectly wired OR the panel is defective; which might be the reason that it had only been "slightly used" in the first place. I tried to download the picture of the wiring schematic you posted but it was too low of resolution for me to enlarge it enough to actually read.

 

Hi guys –

I’m just trying to follow along here (long way to go, I understand about 25% and only about 10% of the diagrams, lol), but wasn’t only the Aquastat (8148) swapped out for the “3250 plus” and the actual zone control stuff wasn’t touched, and in fact it really didn’t need to be touched?

However, since the 3250 is in fact used (possibly bad?), could a flaky 3250 cause excessive current at a thermostat via the T-T connection at the 3250? (Don’t laugh …Alright, it’s OK to laugh a little,lol)

 

No laughing... promise... it's a good question that hasn't been addressed.

No, I do not believe that a bad 3250 could cause problems with the zone valves because that relay cube on the Argo board is the 'endswitch' relay and it ISOLATES the 3250 from the rest of the circuitry.

 

OK, yep – I understand what you are saying. Thanks. Guess it’s just a coincidence that something went wrong just when the 3250 was installed. But I know those kinds of things happen – unfortunately all too often.

 

I'm ruling out the 3250, I think the coincidence is just because it's the start of the heating season and was the first time I turned on that zone since the spring.

I really think that it was just the bad valve head. but I'm still getting that same amp draw of the valve head (1.18-1.22)going through the stat. which may or may not be a problem. I haven't tried it again since I'm nervous and don't really need the heat yet. I'm may just try it, and see if it starts to smell

this got me thinking, but I didn't see anything in the wire diagram that does that. But there's a very good chance I'm wrong here's a close up of the diagram.

 

The Argo panel you have does not isolate the zone valve from the thermostat... you are correct.

With the Taco valves, when the valve first opens you will see a higher amp draw. After the valve opens, the amp draw will 'cycle', they don't draw current continuously once they are open.

 

ya could always throw a relay in there temporarily to isolate the load !!!!
If your worried

 

I may need to do that, or keep an eye out for another control on craigslist. It's a little nerve-racking that when a valve head gets stuck and keeps drawing a continuous load that it'll burn up a stat. since the stats aren't new to the system I know they can handle the excessive amperage, just not for longer periods I assume.

Thanks for the help getting through this guys, I'm pretty sure it's working now.