Aquastat Help Please: Converting to Cold-Start


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Old 10-20-08, 01:17 PM
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Question Aquastat Help Please: Converting to Cold-Start

I have a steel boiler (Thermo-Dynamics S-85) that I am trying to set up as a cold-start. The details of the application and rationale are at the following thread: http://forum.doityourself.com/showthread.php?t=362461. The boiler has an L8124C aquastat. Based on other discussions on this forum, I disconnected the blue wire on the L8124C. I tested the system for a few cycles and it seemed to work fine (i.e., high limit was in effect, but low limit was not; only fired on call from t-stats).
I mentioned this to two heating professionals and they both freaked out! One said that I could burn out the aquastat and that I needed a technician to do additional things to safely convert my system to cold-start. The other guy said that I could burn my house down. Based on these reactions, I have since reconnected the blue wire and I just set minimum low-limit with max differential.
Question: Are these ‘professionals’ correct? Is it safe and reliable to modify the aquastat this way? All of my research (here and elsewhere) says ‘yes’. These heating professionals say ‘no’. Please help.
 
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Old 10-20-08, 03:35 PM
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No comment on the 'professionals' ...

You won't "burn out the aquastat", and you won't "burn the house down".

The problem you will have in modifying the aquastat in that fashion is that in the event something _does_ happen, whether or not it's related to the modification, is you will have voided the UL listing on the a'stat. If it is discovered that this was done during an investigation, your homeowner's insurance company would be within their rights to deny any claim...

If you want to switch to cold start, why not pick up a new a'stat and simply replace it ? Maybe $150 or so ...

I don't care for that modification... when you lift that blue wire, you will disable the burner for a warm start ... BUT, your circulator will now not run on a heat call until the boiler gets above the LL setting... so let's say you've got a cool system, and the boiler gets a heat call and fires up ... the circ won't run right away... the boiler might be at 130° or so before the circ finally kicks on... then, that big ole slug of cool water comes rushing into the warmish boiler. Not sure if this condition on a steel boiler is worse than cast iron, but it's probably just not a good idea.
 
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Old 10-20-08, 05:09 PM
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L8124c

As to your "professionals": As my dear departed dad would have said, "Don't eat that, it's horse s..."

Trooper's comments are dead on. If you don't want to spend the coin & don't mind rolling the dice as far as insurance goes, turn your low limit all the way down & let 'er ride.
 
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Old 10-21-08, 07:01 AM
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Thanks for the quick response, NJ Trooper and Grady. I value your input. Given the possible liability issues down the road, I may just continue to keep it warm during the heating season and switched off Apr-Oct. I am now planning to put in a Biasi (cold start) in the Spring, even though this boiler still has some years left. Tankless coil just doesn't make sense for this application.

Final follow up question: I have set the LL as low as possible (110). Do you agree that the Diff should be set as wide as possible (25) if my aim is to minimize oil use? (Zero demand for DHW-just maintaining vacation house at 50 degrees).

Any explanation is appreciated. Again, thanks for your help; you guys are the greatest!
 
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Old 10-21-08, 04:04 PM
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Differential

I don't think the differential will have any significant impact with the low limit set at 110º.
 
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Old 06-07-13, 11:08 AM
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cold start

There is an easier way to do this conversion,If you take the white diff.wire out, and the low limit wire going in by the dial and wire nut them together it acts as a cold start aquastat! This diagram used to be right on the inside of the cover but I haven`t seen it there in years,probably because at around 200.00 they would rather sell a cold start aquastat!
 
 

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