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Sherlock Holmes at the CONTROL

Ok everybody out there in OilHeat-land

I am trying to help a customer with a particular electrical problem. This is a new customer to me this year however certain clues have lead me to inquire about the durability of a Honeywell L8148 aquastat compared to a L7224U
I responded to a service call for no hot water. The component in question was a Honeywell L8148 aquastat relay in a Weil McLain Gold oil boiler that is over 10 years old. There was a replacement date on the control of 6/14/13 in magic marker on the control cover. There was also a service tag with the same date hung on the boiler by the previous service company. This means that the control in question only lasted 3 years. I asked the customer about this and he remembered paying over $?00.00 for the maintenance and repair several years ago.

I wondered if there is something wrong with the wiring design that may be causing excessive heat to build up inside the control causing them to go bad. This particular control has a burnt circuit board that destroyed the solder connection directly behind the relay that also severed the L2 printed circuit that passes next to the solder connection.

The reason I am interested in this situation is the fact that this boiler is vented with a Field Controls SWG-5s using a CK63 control. There is also a thermal reset in the flue pipe that has been bypassed. Without inspecting every wire individually it appears that the field control is properly wired (with the exception of the thermal switch bypass) because the normal sequence of operation is proper:
1. Call for heat from indirect DHW or other zone closes T T on the L8148 (now replaced by a L7224U)
2. B1 on Aquastat powers up the SWG-5 (Via CK-63)
3. After the pressure switch on the CK-63 is proven air flow the primary control (Beckett electronic) operates the burner motor and ignition and the valve.
4. When the call for heat is satisfied the SWG-5 has a post purge for about 45 seconds.
5. I also simulated a power failure during a call for heat. After restoring power the proper sequence above was normal indicating that the L8248 aquastat was not bearing the load of 3 motors starting at once. (Circulator, Burner, and Vent motors)
So … Did this guy just get a bad L8148 Aquastat 3 years ago …or… can he expect to have this problem every three years or so?
Any Ideas?
Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics


  • ratio
    ratio Member Posts: 3,623
    Watch the inrush current, & also the frequency of the starts. If the motor is slow to start it will pull inrush long enough to heat the traces up, if the contacts chatter or try to restart while a motor is still turning they could arc excessively & get hot. How close to the ratings of the contacts is it running?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    When contacts pull in the only inrush is what powers up the electronic primary. Less than .3 amp. The contacts on the L8148 are not at question. They are fine. The connection of the relay to the printed circuit is what is destroyed.

    To answer your question within 6 to 8 seconds (after the primary control energizes) the SWG-5 has a 38 amp inrush and it drops to 1.4 amps until the burner motor starts 2 to 3 seconds later with a 34 amp inrush and that drops to 2.6 on the B1 terminal of the new L7224u control. So the weak link was the solder joint of the L8148 control.

    Both controls are rated for 7.4 amps with 44.4 Locked Rotor @ 120V and I believe the circuit is operating well within those specifications.

    Since I do not come across this problem regularly is was wondering if the L8148 has has any known issues 3 years ago that would account for the failure or is this going to be a regular problem for this customer

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • ratio
    ratio Member Posts: 3,623
    I see. Issues with those specific controls are a little outside my daily travels, but if there are reoccurring problems and I didn't see anything untoward happening with the motors, I'd install contactors to switch the motors. Better rating & cheaper to replace at the same time.
  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    I have had so many of those controls do that that I have lost count. Usually the burner won't power up. I can take the board loose and almost always put my finger on the bad spot without even looking at it. Always under the relay. If you look close, you will see there is a minimal amount of solder on the pins. Just enough to tack them down. Problems seemed to start about a year after they got outsourced to Mexico.
    I usually just re-solder them and put them back in service. I hate having to replace something that is easily repaired, although I have heard I could get in to trouble for this. Time will tell.
  • BobC
    BobC Member Posts: 5,477
    I've see a lot of failed solder joints and never hesitated to repair them. If movement could be a problem I usually solder a piece of copper braid across the joint to reinforce it; that kind of a fix will never fail. This kind of rework is good enpugh for military gear so I would have no qualms about doing the same to my boiler.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    Great help everyone. I have already replaced the control with the Honeywell L7224U. I have been using this control for about 4 years now and purchased about 15 so far. I have only had one go bad and that was installer error! Has anyone experienced any problems with the electronic control?

    I am giving my new customer all the info and some options to reduce the cycling. Short cycling may be an issue since there are 3 zones: Upstairs, Downstairs and DHW.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics