Help Help Help: No Heat for a Week!

I have not had my typical radiant floor heating system working for a week now and the boiler guys have been unable to find a cure as to why. What they thought was the problem was a 120-24 volt stand-alone transformer gone bad, but when they hooked up a new one, it immediately blew that one. It seems my system has (2) sources of 24 volts that feed the "bus bar" as I call it. However when hooked up, my Taco 705 PC Controller cannot obtain a "target temp" for the water running through my radiant floor and thus quickly kills the boiler. They managed to get everything operation off the systems taco 3 zone relay and internal 24 volt transformer, but still could not get the zone valves to open.

The technicians want to replace the bus bar with something called a Zone Valve Control box, but I have a bit of heartburn about this because the system has worked for 9 years with the bus bar arrangement. I am thinking the problem may lie in a bad thermo sensor. Since the outside temp sensor, and boiler sensors are working proper, I am thinking it must be the sensor on the output side of the mixing valve (circulator).

Any ideas?

Ohm meter and compare resistance readings between other sensors.
They will be different resistances relative to their ambient temps, but can still indicate a problem if expected resistance is too far off or even extreme as in "open" at zero ohms or "shorted" at infinity.

If you can check ohms, then get back to us with your ohms readings matched with their corresponding ambient temp and we'll interpret them.

Check the zone valves, maybe one operator is shorted to ground. You should be able to ring the coil with a meter.

NoSmoke wrote:It seems my system has (2) sources of 24 volts that feed the "bus bar" as I call it.

I recall a conversation about avoiding two different 24v sources when designing my system.

I think I had to use a setting so that only one was providing the 24v and the other was only connected and not providing 24v.

I don't know what your setup is, so can't say too much more about it, other than if there is more than one source, they can cause one or both to fail.

Well the sensors are okay.

I have been making progress as I have located the signal wires coming out of the Taco PC 705 and by running a jumper between them, I am able to get the Taco switching relay to engage and obtain a target temperature assuring me all is fine with the sensors. Everything is running as it should with the exception of the zone valves. I just need to figure out how they are wired into the bus bar and I think I'll have heat. Granted I can just leave the wires off and run the valves in manual mode, but maybe with some online investigating I can figure out how to wire the zone valves properly.

Here is a picture of my operating system complete with a Munchkin Boiler, Taco 3 Zone Switching Relay, and Taco PC705 controller.

Those are Taco 570 series zone valves. They draw more current than a normal motorized zone valve, so you can usually only hook 2 or 3 to a transformer. It is possible that one of the power heads has failed and overloaded your transformer.

Only 3 terminals per zone valve, then can easily be wired up without a control box. I have a few in my system,

http://www.taco-hvac.com/uploads/FileLibrary/100-3.pdf

I do have my heat going, but was never able to get the zone valves hooked up. I just bypassed them for now but at least I have heat flowing to my floors. By the time the concrete slab gets back up to temperature another boiler tech will be here to hopefully get the zone valves wired in...without a zone valve control.

I have nothing against having one, but if one is not needed, I am all about saving parts.

Does anyone know why these type of Zone Valves are so much better?

I dug around on the internet and other then quiet operation and dependability, there is no other explanation. I would think zone valves are all about the same and considering the low temps these ones are to work in, it would not require a more elaborate zone valve.

I ask all this because I am adding another zone for my home and got a typical zone valve and not the 570 zone valve. Before I sweat this guy (or girl) in I was curious if that was going to be a mistake?

The 570 series zone valves open and close slowly, so there is never any noise or banging in the pipes when one closes. They are also supposed to be very reliable, but I haven't don't have enough experience with them to know how long they last. The ones in my system have been working great since I installed them 5 years ago, but the 20 year old Honeywell zone valves are also working fine. You can mix and match different kinds of zone valves in the system without a problem.

One thing about the 570 series, if you are going to manually open the valve for a while you are supposed to disconnect the power wire...otherwise it can burn out the power head.

Thanks Rob, your information was indeed helpful.

In the end we did get it working, with the new zone added. It sounds simple now but there was two problems going on. One was a bad thermostat which probably was shot when the first transformer blew. The second issue we found, which is not really an issue but rather a efficiency thing, is that there must be two calls for heat before the system kicks in. Kind of a third issue was how long the system takes to kick in.

It kind of goes like this, after upping the set temp on the thermostat that kicks in after 5 seconds or so.
Then 90 seconds after that the zone valve LEDs light up indicating they are fully opened.
Then about 5 minutes after that, the system starts in full capacity.

I think we had the wiring right on the terminal block but because of the bad thermostat and 5 minute delay, we thought we had something wrong when indeed it was right. We did end up putting on a taco zone valve control, and while I hate the thought of spending an extra $130, it is nice to see what thermostats are calling and when the zone valves actually open.