House boiler question HVAC experts?

S.Crum

Well-known Member
Hi Folks, Question for you boiler guys. I have a Burnam V90 boiler in my house that uses a Honeywell triple aquastat for control. The system is a 2 zone system with 2 zone valves and 1 circulator pump. Considering fuel oil prices around $3.50 a gallon, I have the system shut down most of the time, I heat the house primarily with a wood pellet stove. In very cold weather the pellet stove struggles to keep up, (or if the pellet stove conks out) it would be handy to have the boiler stepping in to help out. Here's my question, the system is currently wired so the aquastat maintains the boiler temp at all times. When the thermostat(s) call for heat, the required zone valve opens and the circulator pump kicks on, as cold water returns to the boiler the aquastat responds kicking the burner on to maintain the boiler temp. All is well except that it may be a week or more at a time between the extra "help" is required, during this time with the boiler temp being maintained it burns 1 to 2 gallons of fuel a day. Can someone post a wiring diagram that I can change the wiring so when one of the zones is not calling for heat the boiler goes cold? In otherwords when a t-stat calls for heat the zone valve opens, the circulator runs and the burner fires for the duration of the demand until the t-stat is satisfied (or the aquastat is satisfied) then the burner shuts down until the next time one of the t-stats calls for heat. Kinda'-sorta' like forced hot air works.
Thanks for your help!
 
Find the complete Honeywell # on the aquastat, and look up the documentation for it on the Honeywell website. Depending upon the series of control it MAY be as simple as changing a jumper wire inside the aquastat to eliminate the "hot boiler" feature.
 
Not sure how to restrict, but mine is a COLD start, does not maintain boiler temp fires only on THER call. I know if i were to need like yours, would have to change my AQUA-STAT.
 
"I know if i were to need like yours, would have to change my AQUA-STAT."

THAT is unlikely.
 
Go here; (http://nepacrossroads.com/forum-58.html?sid=447f3a8881ec163bf4a4b4210364817a) and ask your question. Who knows, you may even decide to install a coal fired boiler.
 
Hello Bob, Now I'm still confused. I got the documents for the L8124A,C aquastat, the nearest schematic to my system is figure #7 which shows 2 t-stats and 1 circulator. However my system has a separate 24 volt "doorbell" transformer that powers the zone valves and t-stats in a cluster f*^% of wiring that looks like a 10 year old could have done better, but it has worked dependably for 28 years. 2 wires come out of this cluster to the T and T terminals in the aquastat.
Terminals ZR and C2 are not used on my system. The schematic shows B2 and C2 tied together to L2. Can you un-confuse me?
 

Sounds like you are wired off the operating limit only to the aquastat. Many were set up like that years back.

You need to have the zone valve end switches wired into the circuit.

May be best to call a pro in as we cannot see the system or how it is wired.
 
It sounds like you have a domestic hot water coil? I heat with coal, hot water baseboard, but I have the hot water pass thru the oil burner using the circulator pumps that are on the oil burner.
It is not good to let a boiler set for long periods with out some kind of heat to keep the moisture out. I burn my coal stoker all year long for domestic hot water.
 
This boiler originally had a domestic coil but our water has enough minerals to plug a tin milk pail. After a couple years, I put in a big old Vaughn stone lined water heater with a clean out port and unhooked the coil all together (got tired of boiling it out with Sizzle every 6 months). A few years ago the gasket took to leaking so I fabbed a cover plate (that the Burnam dealer thought was worth $54) and pulled the coil and remounted the aquastat in the new cover plate. Life is good!
 
Biggest problem with calling in a so called "pro" is
they are happy to help you out if they installed the
system or can sell you a new system, otherwise they
don't want anything to do with it. Most the local
independents I wouldn't trust to tend a campfire in
the middle of a farm pond.
 

If I'm reading your request correctly, you may be able to wire the control coils of two normally open relays in parallel to the 24v zone valves of the two respective zones. The normally open contacts of those relays would then be placed in parallel with each other (so either one would complete the circuit) and in series with the aquastat circuit.

That way, the aquastat would only be able to start the boiler if one or both of the normally open contacts were in fact closed. The thermostat in either of the zones would energize the circulator pump and the 24v zone valve AND the 24v relay with the N/O contacts. If either one closes it would bring the temp up because then and only then would the aquastat be in the circuit, and if both zones are satisfied, the aquastat is removed from the circuit and the boiler would no longer maintain the temp at the setpoint of the aquastat.

HOWEVER.... do not do this based on this discussion without consulting an on site repairman...none of us here have the luxury of placing eyes on your system therefore any and all suggestions should be considered bogus. There are many things to consider when changing a proven control scheme and things are easily overlooked without having information "in-hand".

That being said, I really wouldn't suggest doing what you want to do at all...consider and outdoor thermostat that will lock out your boiler until the outdoor temp gets to the point that your alternate heat source begins to struggle. It would go in series with the aquastat and only allow the boiler to come on at that outdoor temp setpoint and below. Then again..... refer to the previous paragraph....lololol
 
(quoted from post at 19:19:23 11/24/13)

That being said, I really wouldn't suggest doing what you want to do at all...consider and outdoor thermostat that will lock out your boiler until the outdoor temp gets to the point that your alternate heat source begins to struggle. It would go in series with the aquastat and only allow the boiler to come on at that outdoor temp setpoint and below. Then again..... refer to the previous paragraph....lololol

I have seen a control that changed the set temperature of the boiler according to outdoor temperature, so when outdoor temperature only cool the boiler temperature was not as hot. Then when it got cold outdoors the boiler temperature was hotter.
Perhaps something like that would work for you.

Dusty
 
1. What do you have the "low limit" set at? That is the setting that controls the temp of the boiler when there is NO call for heat. Setting it as low as it goes (just over 100º) will keep the boiler's standby temp as low as possible WITHOUT any electrical changes.

2. See diagram...

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/Aqua_zps8a34477e.jpg">

3. If you can disable that internal connection, the burner will only run when a zone valve is "open". From a cold start, the burner will fire when a zone valve opens and the circulator will NOT start until the boiler reaches the "low limit" setting. (This is for quicker heat exchange warmup to reduce moisture/acid/soot buildup in the heat exchanger.)
 
Yeah, I think Bob is suggesting the closest thing to what you want to do instead of altering the control sequence too radically. It would allow for a bit of a quicker recovery letting the boiler maintaining the lowest allowable setpoint instead of letting it drop to ambient (indoor temp).

Dusty, what you are referring to is a "Reset" control... it allows you to maintain a cooler boiler temp on days requiring only moderate water temp to satisfy the indoor load and proportionately increases the boiler temp as the outdoor temp goes down. The theory is you can more closely match the boiler output to the changing load due to changing outdoor temps.

The "reset ratio" is adjustable on those controls as well...but, then again, please refer back to the second to the last paragraph of my original reply...... Good discussion guys.
 

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