2-zone hydronic, only one thermostat fires the boiler

litedesign

Hi, I just moved into an 1957 house with a gas boiler and 2 circulator pumps. One pump is wired to a downstairs thermostat, and the other to the upstairs thermostat. Currently, the upstairs thermostat only controls its pump, not the boiler. In order to fire the boiler I need to turn on the heat downstairs.

Is this kind of setup normal or is something broken on my upstairs thermostat circuit? Do I need to install a zone switching relay like a Taco 502?

EdTheHeaterMan

Without more information, it is difficult to determine if something is broken. In the past, I have designed heating systems like this on purpose to allow a zone, that otherwise will overheat, to disable the pump once that zone is satisfied using the residual heat from the boiler. It is very rare that I would use this application. Mixing copper/aluminum baseboard and cast iron radiators on the same system is one example. If the baseboard is a “MicroZone” then the baseboard zone will cause short cycling of the boiler. Using this technique would be an inexpensive fix.

The question is, does the zone that does not power the burner have a problem with insufficient heat? If not... then it ain't broke so don't fix it.

However I did say this application is VERY RARE. The chances are someone, not familiar with basic control design, tried to add a zone, or design a zone system incorrectly. I wonder what else is incorrect? Did the designer use flow control valves as needed? Is the piping design even correct? Without more information about your system, It is difficult to determine if you have a problem or if everything is just fine.

Are there any problems with insufficient heat or too much heat in any rooms?

pecmsg

litedesign said:

Hi, I just moved into an 1957 house with a gas boiler and 2 circulator pumps. One pump is wired to a downstairs thermostat, and the other to the upstairs thermostat. Currently, the upstairs thermostat only controls its pump, not the boiler. In order to fire the boiler I need to turn on the heat downstairs. Is this kind of setup normal or is something broken on my upstairs thermostat circuit? Do I need to install a zone switching relay like a Taco 502?

Best to get a qualified service provider to go thru the entire system, insure it’s safe, explain how it works and recommend solutions. 

litedesign

This came from a licensed plumber, he said (without elaborating) that the upstairs thermostat should be able to fire the boiler, and to call an electrician to look at it. Yes, I'm having problems generating heat upstairs, and it seems inefficient to have to heat the basement when no one is down there in order to get heat upstairs. When the boiler is cool, the upstairs thermostat will run the circulator indefinitely without generating any heat.

I guess my bigger question is, is it possible to wire the system for each thermostat to fire the boiler without using a zone relay panel? Because my system doesn't have one of those.

pecmsg

Did this plumber look at the job?

litedesign

pecmsg said:

Did this plumber look at the job?

Yes, the issue I called him in for was that I was getting almost no heat out of half the upstairs system (a 2-branch loop), even when the boiler was hot. It seems the air bleed valves are old and rusted throughout the system, so he recommended draining the loop and replacing all the valves to get the air out of the pipes. But he said I should get the thermostat issue looked at first. I'm just trying to educate myself on the proper wiring so I can negotiate with an electrician.

pecmsg

Sorry but here that’s the plumbers job. 

At the least he could tell what’s wrong. 

It would have helped letting us know that in the beginning 

litedesign

I figured that thermostat wiring was the plumber's job as well. So is there an answer to my original question? Can each thermostat be wired to fire the boiler, or do I need another piece of zone relay equipment?

pecmsg

Several ways to wire it and control it. 

HVACNUT

Could you post some pics of the boiler,  controls, and thermostats?
If it's been like that, and there's no existing relay for the upstairs zone, then I wonder if it's a line volt thermostat and can it be converted to low volt, without running a new wire?

litedesign

HVACNUT said:

Could you post some pics of the boiler,  controls, and thermostats?
If it's been like that, and there's no existing relay for the upstairs zone, then I wonder if it's a line volt thermostat and can it be converted to low volt, without running a new wire?

Thanks. I can post some pictures after work.

How can I tell if the upstairs thermostat is line volt? I can tell you that the wire coming down to the boiler from upstairs is a just small thermostat wire, not a 12-14awg BX or NM or anything like that...

pedmec

how are the low voltage thermostats turning on the circulators? they have to have an existing relay set-up for each circulator.

EdTheHeaterMan

This sounds like the original design was incorrect and not intentional. I gather that from your statement that the upstairs rooms get insufficient heat. Although the fact that there is a problem with getting air out of the system on the second floor can be the major reason for that.

I find that electricians are about the worst at control wiring when it comes to resolving Hydronic control wiring issues. Not ALL electricians but most of them. You are better off with an HVAC company with Hydronic experience. A company that does both gas furnaces and gas boilers, with a dedicated service department, The family plumber that installs the occasional boiler often has trouble with zone controls. I have been the GO TO guy for several local plumbers when it comes to zone control wiring. These guys are excellent at installing bathtubs and water heaters, but control wiring is not what they do.

Try the "Find A Contractor" link above. if there is no one in your area, you can usually find out who is good at control wiring at the local HVAC supply house. Those guys know who is good at what they do and who is not. (I spent 2 years at a local supply house as the "technical support" person for HVAC division). Finding that person who can handle goth the plumbing side and the control design side is not easy. But that person is out there... and he known he is worth a more than the run of the mill electrician or plumber of duct installer.

Good luck in getting your system running properly.

HVACNUT

litedesign said:

Could you post some pics of the boiler,  controls, and thermostats?
If it's been like that, and there's no existing relay for the upstairs zone, then I wonder if it's a line volt thermostat and can it be converted to low volt, without running a new wire?

Thanks. I can post some pictures after work. How can I tell if the upstairs thermostat is line volt? I can tell you that the wire coming down to the boiler from upstairs is a just small thermostat wire, not a 12-14awg BX or NM or anything like that...

Ok, then not line voltage. What is that thermostat wire connected to? You said there's no switching relay, but somewhere a low voltage circuit is controlling a line voltage circulator. 

EdTheHeaterMan

After looking at you post about the C wire for your thermostat, there may be a simple fix to your problem. I need to know what other controls are on your boiler. The X X on the AR862 may be something that can operate the burner on that zone. I just need to know what the boiler control looks like, and this other control model number.

litedesign

Ok, so I spent the morning mapping out my circuits, and I produced a pair of drawings, attached.

Here is what I learned about my system:

1.) The boiler is fired by sending 120V to a transformer mounted on the side of the boiler which sends 24VAC to a gas valve that provides gas into the burner. That 24V circuit has various overheat and thermocouple switches for safety.

2.) I have a relay for each zone, but they are different models:

- The relay for the basement (Honeywell RA89A) has (2) 120V hot terminals: when the relay is closed, one powers the basement circulator pump (12AWG Black), and the other powers the 24V transformer that fires the burner (12AWG Red, which I'm calling the "switch wire").

- The relay for the 1st floor (Argo AR826) has terminals for hot and neutral: when the relay is closed, they power the 1st floor circulator pump (12AWG Black). It's not connected to the Red switch wire that runs to the burner transformer, although the switch wire does pass through the inside of this box on its way to the transformer, as indicated in the drawing.

3.) So if I go into the 1st floor relay box and connect a new wire between the red switch wire circuit and the hot black wire that powers the circulator pump when the relay is closed, then either of the 2 relays will complete the 120V circuit to the boiler transformer and fire the burner. See my red annotation in the "After" drawing.

Does that make sense? I tested it out and it works. Would it cause any problems if both relays are closed on the circuit at the same time? Are there any other long-term electrical issues I should be concerned about with this modification?

Thanks a lot!

EdTheHeaterMan

Can you post the model number of your boiler. that will assist in determining the best way to update your wiring design. and also let us know if the stuff in the circle is at least up the the minimum safety standards as of the date of manufacture. I'm sure you want to know that someone has not bypassed any safety device(s)What's in the green box. Is there a wiring diagram on one of the panels or on the inside of a removable panel?