Low limit aquastat problem

Rookie_3

I had a no hot water call for a very old hot water boiler with a tankless coil. There is a stack relay along with an
845 relay and a low limit(NC) in a well at the tankless coil and a high limit switch. The system runs fine on a call for heat but will not make on a temp. drop at the low limit.I shut the t-stat down and cranked the low limit to max. and still the burner didn't fire. I put a new low limit switch (L4006A) and still no call on temp. drop.
What am I missing? Any and all help is welcome.

Thanks.........Dan

Big Ed

B Aquastat

The old set up was...........The low or B aquastat only control the circulator .When there is a call for heat and the circulator will pump the stored hot water out of the boiler to heat the house . The B will shut off the circulator before it takes all the heated water needed to produce domestic hot water.

You need the B (low)at least 20* lower then the A(high). If the B and the A were too close . The circulator could shut off before the burner will fire. It will put the system in limbo.... No Heat... At least until the boiler cools by it self or someone uses hot water.

The contacts in the A ,high or limit opens or breaks on boiler temperature rise. The B or low closes on boiler temperature rise....

Today with triple aquastats the low is used for mataining enough temperature for hot water production and controling the circulator. The triple has too limits a B and a relay

A L4081 dual aquastat comes two ways, just a A and B and it comes like the triple where the low is also a burner limit but without the relay.....

A old Honeywell set up used in the 50"s was a "series 10 " worked like a triple but used two controls ..

Rookie_3

Ed

This is a mid 50's boiler and is set up in series. The one I pulled was a normally closed low limit making on temp drop. Before the old one quit the system would cycle btween 160* & 200*. The system does not have a reverse acting limit for the circ and would pump cool water on a call for heat. The "A" or N/C I put in is for the domestic from the tankless coil to keep the boiler hot but it is not calling the burner on temp drop. I took a N/C out and put an N/C in,
I just don't get why it won't fire on temp. drop like it was before.
Thanks........Dan

Big Ed

Tankless Being used

Ok it's a little confusing when you use N/C assuming your saying Normal closed . Normally open and normally close is used on relays. Referring to it's contacts when a relay is not energized.....


Breaks or makes on temperature rised is used on temperature sensor controls......

OK first off one problem . Any boiler thet uses a coil for hot water must have a B aquastat..Don't have one ? need one.......

Now the two limits can be hooked up in series . One is the safety while the other is the temperature control. the saftey is always set higher then the operating aquastat..... You will see this set up with a manual reset aquastat...

Another 50's set up...... One of the limits controlling the line voltage to the burner while the other controlling the low voltage through the TT in the primary... I use the line is the safety and the low voltage is the operating. Really does not matter ,depends on the type of aquastat....explained next

Now if the aquastats are in series as you said. Some of them old buggers are slow to operate. Like the old helex type. I would use the helix as the safety and the capulary type as the operating limit..

Better yet if you see this old stuff sell them a new boiler

PS Beware. If you see just a low voltage limit , switch it over to line. If a relays N/O contact stick on a low voltage limit set up . You have a bomb !!!

Also a must be said............. You #@$% around with a limit, test them up ,down and sideways before leave... The life that you save could be your own......

later

Rookie_3

Yes, there is a "B" for the high limit (safety) and everything is line voltage. Also have power to everything and the system on a call for heat works fine. Any way to test the new L4006A to see if it is any good other than by
it not making on temp. drop?
Dan

Big Ed

R845 Setup

Just noticed 845 or R845 relay.

A R845 & 2 aquastats will work like a triple. I feel your problem is in the coil aquastat. That control should be dual acting, like a L4081 or L6006.

Before I ramble on with how it's wired......The " Line" side of a control is the power comming in & the "Load" side of the control is where the power is going....

R845 set up with coil- Power comes in to the load side of the coils dual aquastat. The high side load goes to terminal #1 in the stack relay.The low side load goes to the R845. It can either go to terminal #1 or #3. Sometimes a jumper is used or a direct line...Terminal #4 goes to the circulator .Terminals #5 & #6 are used for the higher limit .Can be powered by it's own line or through a jumper...Should be power going to it all the time. The load of this contact will go to the higher limit and the load of the higher limit goes to #1 of the stack relay....

How this works is the B in the dual controls the circulator through the relay. The A in the dual maintains hot water supply.When there is a call forheat the relay pulls in turning on the circ and kicking the boiler temp up a notch.

The set up works like a Triple.

I think some one did away with the duel and now the load of the A is going to the R845. A L6006 could confuse a novice...

Rookie_3

Thanks for detailing the wiring Ed. This one is wired pretty straight out.........from the service switch line voltage goes to an R845A and to the low limit switch. Low limit to the high limit and from high limit to L1 on the stack relay. 3 on the stack to the motor and ignition.
L1 on the R845 jumped to 3 and 4 is to circ. with the house
T-stat coming into TT and out from 5&6 to the stack relay.
Everything was fine until the low limit (N/C) turned to junk which is probably the case with the new L4006A also. I hit the supply house to try another switch at 4:45pm and they had none left. Nothing like making a bad job worse Huh?

Dan

Big Ed

Wired

The R845 , terminals #5 and #6 go to the stack relay ???? TT in the stack relay ??? ....it will only fire with a call for heat set up that way. As you mentioned

Rookie_3

That is exactly where they go. House T-stat to R845 TT and 5 &6 to stack TT. The system looks old and undisturbed could they possibly have been drawing hot water just off boiler temp. on heat call? Been going all day on 3 hrs. sleep nothing looks right now anyway. Maybe it will clear up over morning coffee. I'm having halucinations of getting thrown out of their cellar.

"Look at this guy, we have been living here for ten years and he just stripped all the wires off our boiler" "we're not paying for this!! Call the inspector!! LOL!

Thanks again Ed I'll let you know what happens.

Dan

oil-2-4-6-gas

hey rookie did you change the well? any heat-conducting compound in there ?

Big Ed

Hot Water

I would think the wiring was changed recently. During the summer they would have no hot water at all.......Someone was there before you....

Rookie_3

Ed

The wiring is exactly like I said above and works OK on high limit and heat call but your right there is nothing calling the burner at temp. drop and the only thing in the R845 getting powered is the circ. off 4 with 5&6 going back to WB on the stack relay. H/O says nothing was changed and shouldn't be, it has been working for 20 years as is. So everything is back to where it was before I got there. Thats the end of this story!! Thanks for the info.

Oil 2-4-6 gas.....Didn't use heat conducting compound, I have in the past and then started hearing talk about nobody
uses it and the boiler has to be drained down and everything bled out to replace the well every time an aqua stat get changed. Bad info? The stuff seemed good to me but I figured the experienced guys knew better. Wrong Huh?
Not using compound worked for me this time since I have the L4406A back in my truck.

ROOKIE