Hi:

First time poster, and a new homeowner. My oil burning boiler (Weil McClain 68 Boiler, model A/B-468U) was being serviced recently, and my oil company installed a new aquastat, because i mentioned that the temperature gauge seemed off (even though lo setting set to 130, temp gauge always read around 180, when no call for heat). Anyway, it looks like they put in a Honeywell Triple Aquastat L6081A (although invoice says installed "dual aquastat"). I believe this is the same model aquastat i previously had. However, i believe the service tech wired it incorrectly. I have attached some photos ( I apologize if the quality is poor).

I have a tankless coil for my domestic hot water and baseboard heating. My understanding is that in the summer months, when thermostat is not "calling" for heat, the Hi setting on aquastat basically does not operate, and the Lo setting operates to regulate temp of water in boiler so there is heat for tankless coil, and this was my experience up until this new aquastat was installed.
However, now when i change the Hi setting, the boiler will come on even though there is no call for heat from the thermostat. So if temp of boiler is 160 and i move Hi setting up to 200 the boiler comes on, even though LO is set to 120 and there is no call for heat. Isnt this wrong? Shouldnt the boiler only come on if temp falls below setting on LO minus diff setting and then cut off when it reaches the Lo setting?

Any help or suggestions would be greatly appreciated.

Thanks!

Chris

 

If there's no call for heat, then the HI limit should not come into play at all. So it sounds like the control is probably wired incorrectly. Without knowing where the wires lead to (pump, burner, etc.) in your pics, it's hard to say for sure what the problem is. For your reference: Honeywell L6081A.

(Hmm... Is it possible that there is a call for heat going on? Maybe the t-stat was left cranked high, or a jumper was accidently left in place?)

Does the needle on the boiler temperature gauge now move properly as the boiler heats up/cools? If not, then the gauge is bad - and you didn't need a new aquastat.

 

Chris, it's possible that it's wired wrong, but Rockledge is right on about us not being able to tell without knowing where the wires are going.

And yeah, for sure I would have suspected the temp gauge LONG before the aquastat. Did the tech actually check that first?

 

Thanks Rockledge and NJ trooper. Would more pictures be helpful with a wider view of the aquastat/boiler? The temperature gauge does seem to work now. Im not sure if the tech actually checked that first, unfortunately i was not home when they were at my house. The thermostats are definietly turned down as low as possible. I apologize, I am very much a newbie- from the wiring diagram for the aquastat i see the reference to the jumper, but im not really sure what it is.

Thanks again for your help.

Chris

 

If a wider shot will show us where the two cables that are entering the a'stat are coming from / going to, then yes, that will help.

Following them and describing where they go might too.

Is there a manual for your boiler still around there somewhere? If so, is there a wiring diagram in that manual? If not, we can look on the W-M website and see if they still have docs for your boiler on-line... they usually do.

The 'jumper' is that rectangular thing between the two 'R' on the bottom of the a'stat.

Sort of... the DIFF setting on the LO limit is a little 'funny' ... reference fig 10 in the data sheet that Rock posted a link to.

BOTH the HI and the LO have a FIXED negative 10°F diff built in. The boiler should always fire up when the temp drops 10°F below the LO setpoint regardless of the DIFF dial setting.

The DIFF dial ADDS to the negative 10 fixed diff.

Example: LO set 140 , DIFF set 25

Boiler will fire at 130 ( LO - fixed 10 negative diff ) and stops firing at 155

( (LO - fixed 10 negative ) + 25 ) = 155

In other words, the BOTTOM of the range will always be the LO setpoint MINUS 10.

The TOP of the range will always be the BOTTOM PLUS DIFF.

 

The docs for the 68 boiler on the W-M site only show a newer a'stat relay, the 8124 model.

See what you can tell us about the destinations of those wires.

 

Just to clarify, I was referring to the case where the "TT" terminals on the aquastat are manually jumpered by a technician in order to initiate a "call for heat" (for testing purposes).

The jumper referenced in the wiring diagram is something else entirely.