No Zone 2 Heat, Old System, Stat calls Boiler won't fire but Zone 1 Works Perfectly.

MODZISTER

I have an older system that I just repaired 1 week ago. It's a very basic setup 2 zones 2 pumps that run off 2 different 20+yr old zone controllers or Aquastats whatever there called. This system has no zone valves. I'm an Electrician not an HVAC person so everything about my system I learned in the past week. I do things by very strict guidelines for myself if I can't do it the right way I won't do it at all. I think that's important to know.

The problem one of the zone pumps flooded my basement while I was at work. I replaced the zone 1 pump and replaced both zones gaskets and bolts while I was at it cause they both had slight leaks and bleed the air out of the system. After doing that both stats called for heat and fired the boiler. I noticed zone 2 wasn't getting hot so I tried bleeding the air again and after that it won't fire the boiler anymore. Maybe just bad timing? I'm not sure. When I bleed it the system was off obviously.

So basically we have zone 2 Thermostat calls for heat the zone pump kicks on but won't fire the boiler. The electronics are that old that I'm not sure what I'm even looking at I'm not sure if there is something that I can try that somebody here can see from the pics. The only thing I tried was swapping the Thermostats that did not work. The only other thing I do know in the controllers is the 24vac transformers but all they do is power the thermostats idk what the other switches are with the springs on them.

EdTheHeaterMan

Zone 2 stat controller is the wrong controller. That Honeywell Switching relay is the most basic model. Your system requires the R845A with an additional set of contacts.

Your control does not have the relay contacts that connect to terminal 5 and 6

That additional set of contacts will be needed to operate the oil burner by way of the ZR terminal of the R8182 zone one relay control.

Here is the diagram:

LRCCBJ

Ed, since it is only two zones, I don't see why he can't run a single wire from the circulator output in the 89 to ZR in the aquastat.

Of course, would need to come off the 89 with a single wire and then have a junction into the circulator lead and the aquastat (ZR) lead.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1837925#Comment_1837925

That will bring on the burner… but the circulator on zone 2 will continue to run when the boiler temperature drops below the low limit. That feature is built into the design of the "Figure 3" wiring diagram. As the system is now, when zone 2 calls for heat when you are taking a shower, the cold water from the radiators will enter the boiler and you may end up with insufficient DHW. By using the ZC to stop the zone 2 circulator from operating when the boiler temperature drops below the low limit, the burner has a chance to recover before turning on the circulator pump on for both zone 1 and on zone 2. that way there are n ocold showers

LRCCBJ

Yes, agreed………..with a tankless coil you need the 845 to prevent that.

I suppose he could try it as an interim solution.

I had one building without any connection between the 89 and the 8124. The building was small enough so it really didn't matter.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1837930#Comment_1837930

This happens often. and when you get used to doing it this way without any negative repercussions, you dont think twice about this incorrect wiring job. Then you may not realize that your customer is actually experiencing the cold shower problem. As the coil calcifies over time, The problem becomes more and more of a problem. The problem is then diagnosed as a poor design to begin with and a separate water gets installed. But the L8182 control still maintains boiler temperature that is wasting fuel. I have seen this too many times. Electric water heater 2 zone boiler maintaining 160° for the zone 2 pump and high oil usage and high electric usage.

The best practice is to install the tankless coils with easy to connect maintenance valves (like those recommended on wall hung tankless water heaters) and the proper zone 2 control connected to ZC and ZR on the zone 1 control. But that would mean that plumbers would need to know how to do this when they add a zone to a boiler with a tankless coil. …unlike the plumber that was at @MODZISTER's location many years ago and just added the pump control because "the boiler is already hot anyway so you just need to pump that hot water to the new baseboard heaters"

MODZISTER

Wow, So this is not setup right in the first place. How was this even working before and what would be the reason it's not working now? What can I try to make sure that whatever is the problem is the problem.

Also would it be worth just getting something newer that I can connect everything to in one box instead of it running off 2 seperate controllers. Or should I just get that Honeywell R845A and hook that up for my zone 2.

Thanks for all the help and feedback so far.

LRCCBJ

Presumably, it is working now. It just won't go to high limit when the second zone calls. The boiler should start when it's temp gets down to 160° (irrespective of a the thermostat). If you have hot water, the boiler is working exactly how it was working before you changed the pump.

You might be fine with 160° depending on how much baseboard is in the zone.

No, you just need a proper relay for zone 2 and wire it to the existing aquastat.

MODZISTER

Oh ok I think I understand what your saying now. I just now set my zone 2 thermostat to 65 degrees the pump kicked on but the boiler didnt fire cause the temp is already above 160 and only when the boiler gets below that it will fire. Wow what a strange setup so does that mean it wouldn't matter what I set the thermostat to if my zone 1 is hot enough it won't let zone 2 get any hotter. Does that make sense, That's basically what's going on here?

EdTheHeaterMan

@MODZISTER : I remember taking a class in how heating systems work over 40 years ago. That is how I know that your system was set up incorrectly 20 years ago. the fact that you hsve been using it that way for the last 20 years means the you are ok with the way it works, and you may just be used to the small inconvenience of the hot water temperature drooping a little, if you even feel it at all.

I also see that you do not have a mixing valve on your DHW coil. So you have also become accustom to the changing hot water temperature from your tankless coil. I would think that you are constantly adjusting the amount of cold water you mix with the shower water as the boiler goes thru different cycles in the summer and in the winter.

Let me look thru my files to get you the explanation of the sequence of operation of a boiler with a domestic hot water tankless coil. Be right back.

MODZISTER

Sounds good thank you. We never really used the heat very high cause it never works that well we actually use space heaters in the winter that's how bad it is but on zone 2 the 2nd floor it used to work decently well but now that I changed that pump that I assume prolly didn't work for a long time our 2nd floor heat isn't working. I turned on the 2nd floor thermostat but it's still ice cold that's not the 1 I changed I changed zone 1 pump. Maybe now the zone 2 pump is bad I hear it come on so I know it's running or maybe I need to bleed the system better.

EdTheHeaterMan

Yes there is most likely air in the system. Do you have baseboard heaters that are made of copper tubing with aluminum fins?

this video explains it pretty good. Watch until you see the part about purging the second floor.

https://www.youtube.com/watch?v=z80WspC4Nmg&t=82s

MODZISTER

yupp baseboard heat exactly. When the pump turns on you can hear the water run through like it's pushing air

MODZISTER

For your description there at C that's a valve? I didn't even know that so I turn that set screw in to close it. I knew about using fast fill but yea I never closed that valve I was wondering why there wasn't a shut off above the pump but below the faucet. I guess there is I should of took HVAC just to have some of the knowledge.

EdTheHeaterMan

Here is the explanation of how the L8124 and the R8124 controls work.

This is a detailed explanation because the L8124 and the R8184 controls are a little complicated and the instructions that come with the control explains it in a very technical way that is hard to understand for many of us that work on boilers, and harder for the average Joe

so I tried to make it simpler here.

When you have a tankless coil in a boiler for domestic hot water there are many different temperatures that will happen during the different boiler system cycles.   Let's start with the summertime when you do not send heat to the radiators. 

• The boiler maintains a minimum temperature so when you are using the hot water any cold water that enters the coil will be hot water by the time it exits the coil and heads to your shower.  
• In order to do that some basic math is needed. 
• You need to know the gallon per minute flow rate of the water in the coil
• You need to know the incoming water temperature of the cold water
• You need to know the desired water temperature (usually 120°F) you want at the shower. 
• With that information you can select the minimum water temperature you need in the boiler to achieve that goal. 
• In your case someone has determined that you need 150° in the boiler to get 120° at the shower.  
• So they set the low limit  to 160° with a differential of 10°.  This means the burner will run if the water is below 150° and stop running when the boiler water gets to 160°

With that information we can plainly see that you may get hot water at the shower as high as 160° and as low as 120° during a summertime boiler cycle.  Here is how that happens.  

• The burner operates to get the water temperature to 160°
• No water is moving thru the coil so that water in the coil will eventually get to 160°
• If you open the shower valve, that 160° water will push the room temperature water in your pipes between the coil and the shower head out of the way and you will get cool water, then 160° water for about 30 seconds.   
• Once that 160° water is out of the shower head the cold water that was heated by the coil in the boiler will drop to say 130°  because the boiler water around that coil is still 160°
• As the boiler temperature drops to 150° the cold water will only get to 120° and the burner will come on to heat the boiler water. 
• As the burner operates the boiler water will increase to 160° and the shower water will rise about the same 10°.  To 130°
• This will continue for the duration of the shower.  The water in the shower will go from 120 to 130 and back to 120 as the burner cycles.
• This constant changing will result in your turning the cold valve the manually to keep the water temperature that goes above 120° from scalding you. 

This same process happens in the winter with the addition of the circulator pumping cold radiator water into the boiler and pumping hot boiler to the radiators.  The 8124 control stops the circulator from doing that if the boiler water drops below 150° and allows the circulator to operate once the boiler water temperature reaches 160°  Eventually the return water from the radiators is hot enough to keep the boiler water from dropping below 150° and eventually the boiler water temperature may increase as long as the thermostat calls for heat.   If the boiler temperature climbs to the high limit on your control at 200°.  The circulator will continue to pump 200° water thru the boiler and the radiators as long as there is a call for heat.

Now think about the hot water in the coil at 200° and no one is using any hot water.  That water in the tankless will reach almost 200°.  Now someone will turn on a hot water tap in the kitchen to wash their hands and a little room temperature comes out until the 200° tankless coil water reaches the kitchen sink and BAMB! 200° water is coming out the faucet.  What a surprise that is for that person.

But you are used to that because that is the way it always was and always will be. And that is because the original installer did not have time to read the installation instructions that require a tempering or mixing valve on your DHW system.  here is an instruction manual diagram from a 60 year old boiler. The manufacturers required it long ago and they still require it today. Your boiler is not up to 60 year old requirements.

Then when the second zone was added, there was another factor added, zone 2 pump does not stop when the boiler temperature drops below 150° and that makes your system just that much more unpredictable in the shower. 

Hope this helps you to understand your system a little better.

MODZISTER

That is very accurate because if you use the hot water and a few minutes later you wash your hands or something you absolutely get burned it's that hot extremely hot I guess that's because the water is 200 degrees wow so they couldn't even do it right according to 60yr old practices. It seems you know this very well and it's pretty common to find a setup like this in older homes.

Well hopefully bleeding it get's the heat working again on the 2nd floor. I'm gonna save all those write ups aswell. I appreciate the help and I will let you know if it works after.

EdTheHeaterMan

When you get the mixing valve installed, you can find a consistent water temperature at the faucets and shower head.  That is because the mixing valve will measure the hot in temperature and add just the right amount of cold to it in order for it to leave the boiler room at 120°. 

Here is one Mixing valve that will work for you.

LRCCBJ

@MODZISTER

It seems you know this very well and it's pretty common to find a setup like this in older homes.

He does. He's the master of all the old controls (which you have).

MODZISTER

Can someone just confirm that C in the picture is a valve and I just turn in that screw to close it when I bleed it?

neilc

do you see any markings on those valve flange things? any names?

then we google from there

neilc

MODZISTER

I bleed the system and the heat is back to working normal. There was alot of air in the zone 2 piping. It's working as good as the system will allow the way it's installed. I learned alot and I see some potential upgrades or things that should of already been installed to begin with planned for the future.

Thank you to all that have helped through this process I really appreciate it.

LRCCBJ

Excellent!

If the second floor stays warm enough, you don't need to bother replacing the relay.

You really should consider the tempering valve unless everybody in the household is thoroughly cognizant on how the system works and the fact they will get 170° water from the showerhead once that slug of water in the coil reaches their shower. It's really a bit dangerous for most people.

With the valve, you get 120° water all the time………..independent of the boiler temperature. You just take a shower with the shower valve at just about full hot. The entire family will appreciate it!