Aquastat question

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McKraut

McKraut

Feeling the Heat
Sep 1, 2011
349
South Central PA
I have an Aquasmart 7600A controlling my oil boiler. I have the aquastat set so that there is no low limit, the high limit set to 195*F and the high differential set at 20*F. When the wood boiler can't supply enough heat the oil burner should kick on and start to heat water. It doesn't. The only way I can get it to fire is to set a low limit. I don't want it to keep the boiler warm when the wood burner can do that. I thought the only time you had to set a low limit was when you were heating DHW (which I am not).
Can you tell me what I am missing?

Bob
 
I doubt I can help you, but I seem to be missing a thing or two from your post. It sounds like you want your oil furnace to kick in when your heating loop water drops below a certain point. I don't really understand how that is any different in principle from heating DHW. I would still expect to set a low limit at which the oil furnace would kick in.
 
How is T-T call for heat activated when wood boiler falls behind? Boiler won't cold start unless there's a call for heat.
 
Last edited:
Rory said:
I doubt I can help you, but I seem to be missing a thing or two from your post. It sounds like you want your oil furnace to kick in when your heating loop water drops below a certain point. I don't really understand how that is any different in principle from heating DHW. I would still expect to set a low limit at which the oil furnace would kick in.
Click to expand...

I think he means going cold-start. I.e., when the heating loop water is above setpoint, the oil boiler just doesn't fire & goes cold. Some oil boilers keep themselves hot even with no call for heat when heating DHW (like when using an internal DHW coil) using the low-limit settings.

I think.
 
I have a separate strap-on aquastat tied to my storage tanks to fire my oil boiler. That might be your best bet here, but on the supply out of the wood boiler.
 
The system was designed (as I understand it) with a Tekmar controller with the wood boiler being primary and the oil being secondary. When the primary can't supply sufficient heat, a zone valve closes signaling the secondary to fire. I wanted to keep the secondary as a cold start because I don't want to waste oil keeping the oil burner at 100* when the wood burner is active. There is no DHW set up with this system (yet). I only have an elementary understanding of all this stuff, so if you can dummy down your responses I'd be grateful.
 
Ok, no worries there, cause I didnt know anything until I started reading here, and I still dont know much.... :P

There has to be something that would close the zone valve, and trigger the secondary to fire. The cold start part of the boiler should be a separate set of controls.

For instance, I have a cold start boiler, and all of that is controlled by a Honeywell controller on the oil boiler itself. I bought a separate controller that intercepts the signal from my Taco Zone control to the oil gun. When my strap on aquastat is warm, it doesnt let the oil fire, and opens a zone valve/starts a pump to feed the house from storage tanks. When the tanks are cold and there is a call for heat from a T-stat, the oil boiler runs as it would if I didnt have a wood boiler.

Im not familiar with the Tekmar, so if you can post a model number, we might be able to figure out what you need to do next.
 
With the low limit set to off, the Aquasmart will need a call for heat. That call for for heat can be closing the T-T terminals or powering ZR with a line voltage signal. If the burner isn't firing, assuming it's wired correctly there is no "call for heat". What generates a call for heat?
 
Clarkbug said:
Ok, no worries there, cause I didnt know anything until I started reading here, and I still dont know much.... :p

There has to be something that would close the zone valve, and trigger the secondary to fire. The cold start part of the boiler should be a separate set of controls.

For instance, I have a cold start boiler, and all of that is controlled by a Honeywell controller on the oil boiler itself. I bought a separate controller that intercepts the signal from my Taco Zone control to the oil gun. When my strap on aquastat is warm, it doesnt let the oil fire, and opens a zone valve/starts a pump to feed the house from storage tanks. When the tanks are cold and there is a call for heat from a T-stat, the oil boiler runs as it would if I didnt have a wood boiler.

Im not familiar with the Tekmar, so if you can post a model number, we might be able to figure out what you need to do next.
Click to expand...

Thanks for your offer. I am using the Tekmar 401. Would it help if I sent you the schematic for the piping and wiring?
 
R Mannino said:
With the low limit set to off, the Aquasmart will need a call for heat. That call for for heat can be closing the T-T terminals or powering ZR with a line voltage signal. If the burner isn't firing, assuming it's wired correctly there is no "call for heat". What generates a call for heat?
Click to expand...

My assumption was when one of the zones called for heat, that would generate a signal from the Tekmar. Sorry, but I don't understand all this stuff. It was generally explained to me when the system was being designed. The guy who designed it is now out of business.
 
ewdudley said:
I did, actually. The OP is trying to run his boiler as a cold start boiler with no low limit. How is your link helpful in his situation?
Click to expand...
Thinking I'd be asking that question at that site as this is their level of expertise..

Ray
 
McKraut said:
Would it help if I sent you the schematic for the piping and wiring?
Click to expand...

If you have these available, that would be very helpful!
 
McKraut said:
Sorry about the delay in responding. Last night the wind was blowing and our internet is spotty when it's blowing (no, I am not kidding).
I just got back home work. I attached the schematics for the plumbing and wiring. Your insight is appreciated.
Bob
Click to expand...
Now we're getting somewhere. I guess first step would be to make sure that "Simple Toggle Switch To Disable Wood Stage 2 Boiler Heating" is not off. (Which is the oil boiler call for heat disable switch, if I'm reading it right.)
 
Yes it is off.
I was pitching a fit the other day when I couldn't figure out what was going on. The first question my wife asked me was "you didn't forget to flip a switch or something dumb like that' -- (now you have to say that with endless love and sarcasm to get the full effect). I immediately said "Of course not", then after she left the basement I ran upstairs to make sure it wasn't off.
 
McKraut said:
Sorry about the delay in responding. Last night the wind was blowing and our internet is spotty when it's blowing (no, I am not kidding).
I just got back home work. I attached the schematics for the plumbing and wiring. Your insight is appreciated.
Bob
Click to expand...

No worries. My internet is the same way.

EW makes a good point, check your toggles.

Looks like the oil boiler call for heat is triggered by the position of the three way zone valve. Not clear to me what automatically triggers that, but I'm typing from my phone....

Try and disable the wood boiler via toggle switch and see if that cycles the zone valve and enables the oil boiler.
 
In the wiring diagram they're showing a a "Boiler Supply Temperature" sensor input into the Tekmar 401, but it does not show up in the system diagram (it goes to the Azel display instead!). The only way I can see that the Tekmar would know that the wood boiler has cooled off would be that sensor, so without the sensor, no "Stage Two" oil boiler activation (via the three way zone valve).

[Edit:] Never mind, they've got not one, but two "Boiler Supply Temperature" sensors...
 
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When I disable the wood boiler via the toggle switch to the wood boiler:
  1. If the Tekmar says boiler 1 (or no boiler) is calling for heat, nothing happens.
  2. If the Tekmar says boiler 2 is calling for heat, the three way valve closes and:
  • If the low limit is set, the oil burner kicks on
  • If the low limit is zero, nothing happens
Bob
 
ewdudley said:
In the wiring diagram they're showing a a "Boiler Supply Temperature" sensor input into the Tekmar 401, but it does not show up in the system diagram (it goes to the Azel display instead!). The only way I can see that the Tekmar would know that the wood boiler has cooled off would be that sensor, so without the sensor, no "Stage Two" oil boiler activation (via the three way zone valve).

[Edit:] Never mind, they've got not one, but two "Boiler Supply Temperature" sensors...[/quo
ewdudley said:
In the wiring diagram they're showing a a "Boiler Supply Temperature" sensor input into the Tekmar 401, but it does not show up in the system diagram (it goes to the Azel display instead!). The only way I can see that the Tekmar would know that the wood boiler has cooled off would be that sensor, so without the sensor, no "Stage Two" oil boiler activation (via the three way zone valve).

[Edit:] Never mind, they've got not one, but two "Boiler Supply Temperature" sensors...
Click to expand...

The temperature sensors are there only for informational purposes. The Azel is inside the house so I don't have to walk out to the shed every time to check the temps.
Click to expand...
 
McKraut said:
When I disable the wood boiler via the toggle switch to the wood boiler:
  1. If the Tekmar says boiler 1 (or no boiler) is calling for heat, nothing happens.
  2. If the Tekmar says boiler 2 is calling for heat, the three way valve closes and:
  • If the low limit is set, the oil burner kicks on
  • If the low limit is zero, nothing happens
Click to expand...
I'm pretty sure you've proved that the sensor is working, the Tekmar is working, the three way zone valve is working, and the zone valve end switch is working, and therefore the problem is in how the aquastat is programmed, which is pretty much what you were saying two days ago. Give us a while to study the Aquasmart modes of operation.
 
ewdudley said:
I'm pretty sure you've proved that the sensor is working, the Tekmar is working, the three way zone valve is working, and the zone valve end switch is working, and therefore the problem is in how the aquastat is programmed, which is pretty much what you were saying two days ago. Give us a while to study the Aquasmart modes of operation.
Click to expand...
OK. Thanks a lot. I will check in tomorrow night when I get home from work.

Bob
 
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