Replacement for old aquastat

SweatyInToronto

A Honeywell LA409B just bit the dust, and it looks really old maybe 1950s, 60s?
Do any old-timers know the part that should be used for it, if we just want to replace it?

It seemed to control the boiler pumps, but never shut them off. Then one day it did shut them off, but for no reason. So we bypassed it for now. There are high limit controls on each boiler. And there's a tekmar 261 control, that I think would be enough to turn boilers on and off based on the reset curve and differential.
They recommend an 082 sensor only. So I'm not clear if this was a substitute, and I should replace it with the 082. The wiring is really tricky but I'm hoping to have someone over to figure it out, and soon.

Robert_25

It is an old make on rise aquastat.  It may have been used to prevent the circulators from running until the boiler was above condensing temperatures.  What temperature was it set at?

SweatyInToronto

It was on the circulation supply end and controlled the boiler pumps, not the circulation. Using it the way you say makes more sense but we don't really have a primary-secondary setup. All return that goes into the boilers ends up in circulation. I was told it was high-limit so I'd guess it was at 180-200. It was about 12 feet up so I didn't see it myself...

EdTheHeaterMan

New "Old Stock" still available for sale. look on eBay and other sites. This is a Make of temperature rise control. also known as a "Reverse Aquastat"

The modern-day replacement is an L4006C 1018 use the R and W terminals (Will Run on temp rise)

R and B terminals are for open on temp rise (Will Break on temp rise)

EdTheHeaterMan

@SweatyInToronto your reply to @Robert_25 makes incorrect assumptions. When he said "Circulator" he was referring the pump that circulates the water thru the closed system.
check this comment for reference and look at the whole discussion for that matter It gets quite entertaining at points

https://forum.heatinghelp.com/discussion/comment/1616191#Comment_1616191

SweatyInToronto

Ok we have 3 circulators pumps. I guess they all circulate it through the closed system. One is primary in the sense it's the largest and moves water from the radiators and back to them. 2 are secondary and smaller and just move water through their respective boiler.

The reverse aquastat was wired to the 2 pumps that move water through the boilers. Its sensor was on the primary supply but controlled the secondary pumps. If these pumps don't run then there should be no or minimal flow through the boilers and water wouldn't heat up, so I don't see how they could only be switched on when the water temp reached 140 degrees for example. Water would never get hot unless they were running.

Are both models always a reverse type, eg -1071 or -1006? Not sure which one we have yet - may have to take it off completely.

EdTheHeaterMan

First of all, the LA409B has very little in it to go wrong. Temperature sensing bi-metal helix coil that rotates based on temperature and a mercury switch that makes or breaks based on the level of the mercury bulb. What exactly went wrong with the system and how did you determine the LA409B is the cause of the failure.
Also your terms Primary and Secondary are ambiguous without a proper reference.

If in fact, you have a true Primary / Secondary system design, The Primary loop is the one where the expansion tank is. Since that could be on the boiler loop or the radiator loop depending on the system, we like to call the Circulator Pumps by different names. The pump that circulates the water thru the boiler is called the boiler pump and the pump that circulates the water thru the system is called the system pump. The pump that circulates boiler water into an indirect water heater is called the DHW pump (for Domestic Hot Water) if you have a modern boiler control the control may have different points to connect these pumps. Since you have an older system (evidenced by the LA409 control) then the wiring and logic of the system may be somewhat different based on the original design of the installer ... so many years ago.

We can't tell you why the control is there, but we can tell you that it is a simple switch action (On-Off) that makes on temperature rise.and breaks on temperature fall with about a 6° to 10° differential Also the accuracy od the control is based on the control being perfectly level. The is the mercury switch has to be exactly horizontal. Any pitch clockwise or anti-clockwise will affect the accuracy.

Robert_25

If these pumps don't run then there should be no or minimal flow through the boilers and water wouldn't heat up, so I don't see how they could only be switched on when the water temp reached 140 degrees for example

Are you sure you mapped out the control wiring properly?

SweatyInToronto

Not sure about a lot about this system! 

The control failed in some way because it turned off the boiler pumps for no apparent reason.  Up until that point the boiler pumps ran 24x7 even during WWSD. They would not go on until the control was bypassed by the electrician, temporarily.  However even though while the boiler pumps were off the boilers were firing and overheating.  So the wiring is not ideal for sure...hope to find a local expert can sort it out and improve it in the near future. 

I'll get it pulled off tommorow and have a closer look and let u know. 

Thanks much for your feedbacks! 

mattmia2

Were the boilers overheating? Perhaps they are set up as warm start and an aquastat keeps them at some temp all the time and weather or not the heat from the boiler goes in to the system is controlled by if the boiler pump is on or not.

SweatyInToronto

Seems that it was a left over aquastat from a conversion to from oil. It was wired to shutoff the boiler motors at a high limit - not turn them on. When it failed, for whatever reason, the boilers still fired but without enough flow. They have their own high limit shutoffs L6006A which then would kick in and restart based on the differential.

So this case is closed for now.

Thanks all for your thoughtful inputs!