Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Thermostat directly connected to burner, not aquastat?

I previously posted this question in Oil Heat, but it didn't get much interest there so I am trying again here.

My boiler is set up with what I think is an unusual wiring configuration: the L8124 a/c aquastat has its own TT terminals jumpered, and the thermostat goes directly to the TT on the burner control (R8184G I believe). The burner power is still connected to B1/B2 on the aquastat. As I understand it, this has the following effect on the complete system compared to normal cold- or warm-start operation:
Temp < LLLL < temp < HLtemp > HL
No call for heat Cold start: Circ off, Burner off
Warm start: Circ off, Burner on
Modified: Circ off, Burner off
Cold start: Circ off, Burner off
Warm start: Circ off, Burner off
Modified: Circ on, Burner off
Cold start: Circ off, Burner off
Warm start: Circ off, Burner off
Modified: Circ on, Burner off
Call for heat Cold start: Circ on, Burner on
Warm start: Circ off, Burner on
Modified: Circ off, Burner on
Cold start: Circ on, Burner on
Warm start: Circ on, Burner on
Modified: Circ on, Burner on
Cold start: Circ on, Burner off
Warm start: Circ on, Burner off
Modified: Circ on, Burner off
That is, it behaves mostly like a cold-start except that it circulates if and only if the temp is > LL, regardless of call for heat.

I spoke to the guy who set this up (it came with the house) and his rationale was that the previous owners complained about the far radiators still being cold when the heat turns off and he figured he could address that issue by continuing circulation past the call for heat. And the tankless coil just feeds to an electric water heater, so removing the warm start functionality does not reduce the availability of hot water in the house. The manual for the boiler (New Yorker AP-490U) seems to say that it is also available without a tankless heater and in that case it is cold-start, so it seems to be safe to let it get cold.

Am I understanding this all right? Is this something that is done often? Is there some other disadvantage to this setup that I am not thinking of?


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Still wrong. Basically the same response as in your last thread.

    Power is constantly being sent to the burner thru B1, and comes on when the thermostat calls for heat. Even with a modern primary control, you would add a separate wire for constant power (for post purge and on-board diagnostics), but T-T would be jumpered on the primary (physically or internally, and NOT jumpered on the aquastat.

    The rational is the boiler won't maintain temperature because the thermostat is not calling, which is good-but only in theory with the current wiring.

    It's better to change the aquastat to a cold start or a modern aquastat like the Hydrolevel 3150 plus and wire it correctly, taking advantage of thermal purge, circulator hold off for low return water temps, and even the added benefit of a LWCO (changing the well).

    The problem really boils down to if you get a run-away boiler/burner, and it damages and/or burns your house down, and the unit isn't wired per manufacturer's recommendation/instruction, you assume the liability.
    It is really worth it to not easily do it correctly?

    There was an error rendering this rich post.

  • hundt
    hundt Member Posts: 5
    Thanks STEVEusaPA, I really appreciate you responding (again).

    I am definitely a by-the-book type of person, so I would not have wired it up this way by myself, and if I were replacing it I agree that it would be better to have a modern hydrostat, wired according to its design.

    On the other hand, I'm just a homeowner, and an experienced professional did install it, so I'm hesitant to complain to my oil company, or find another oil company, over this unless I can identify a concrete risk or problem that this setup is causing. In terms of safety, I am unable to come up with any combination of faults (shorts, failed safeties, etc.) that would be dangerous with this wiring but not the standard wiring.

    So I posted this question to see if I was missing anything, but so far it sounds like I am not: this is not the way the hydrostat was intended to be wired, but there is nothing inherently wrong with the behavior of the resulting system.