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aquastat repeat trip (burn out) - why?

I have a weil mclain oil boiler < 10 years old
Beckett Motor and now a honeywell aquastat board (we had a different digital board before - not sure of the brand).
Last week we lost power overnight. When it came back on, the furnace would not start.
Service guy came out identified that the digital aquastat was tripped. He identified it in about 10 seconds. He unplugged one of the wires. He identified that the wires are flimsy and he did not like that style. plugged if back in, it started up and then it tripped again.

He identified it as bad wires and "you cannot just replace the wires" so he installed the honeywell aquastat L7224 (universal model).

Three days later again no heat or hot water.
Comes out and says a circuit on the Honeywell aquastat board was bad.
Assumed a bad board and installs another Honeywell Aquastat L7224.
6 hours later, we are out again.

Something is causing too much juice to the aquastat board. I had the electric company check voltage coming to the house - no issue. Had an electrician friend check all of the connections from the panel to the boiler. Everything looks in good shape.

Any ideas on what could be burning out the aquastat?


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,979
    edited April 2020
    Digital aquastats dont 'trip'. Bad wiring, bad neutral, power is not clean, or just a bad aquastat.
    Sounds like more in-depth troubleshooting and testing is in order.
    'Assumed', and 'looks in good shape' aren’t words from competent technicians.
    rick in AlaskaSuperTechZman
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,989
    You are experiencing an intermittent dead short external to the L7224 control. Since it does not present when the technician is there to see it happen, you will need to add some inline fuses to the B1- terminal and the C1 terminal. If you have zones that use the ZC and ZR terminals you should also add inline fuses on those terminals also. When no one is there and the intermittent short presents, the fuse will fail and the control will be intact. follow the blown fuse to the problem. Automotive fuses 5 amp or 7 amp should do the job.

    After the short is located... Remove the fuses. They are not designed to be permanently installed on the line voltage system
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • jollyhombre
    jollyhombre Member Posts: 3
    what does power is not clean mean? I am not technical in this area by any stretch, so any details are appreciated.

    Wiring was confirmed to the house and all of the connections from the panel. Wires, insulation, connections were clean and tight.
    Digital Aquastat was in for a number of years with no issues. All of a sudden after power is out, the digital is not working. He unplugged the main wire to the aquastat and plugged it back in an the boiler fired on. a few seconds later it shut down.
    2 Honeywells blew a "circuit" (C1?) on the board (1 took 3 days, other hours).

    I do not think its the aquastat
    I was told that a bad neutral would also burn out TVs, computers and anything digital. Is that correct?

    Thanks for your time
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,989
    edited April 2020
    So that means the problem is in the wiring to the circulator. Look at the wire connections under the circulator wire junction cover. As the system heats up then cools down, pipes wires and other components expand and contract. This slight change in size can be the reason for the intermittent chance of the power wire to a dead short.
    Dead Short is where hot and neutral wires are connected without a load Picture a paperclip placed in a receptacle and the resulting spark will trip the fuse or circuit breaker.

    This may also be a resistive short. That may be a bad motor winding on the circulator pump. Not completely failed yet but as it operates and the windings heat up, something expands and a very thin section of insulation allows a fraction of the electric current to pass where it should not pass. This causes the wiring to heat up and the circuit fails at the weakest connection.

    while typing this is thought of another possibility. did someone use the wrong size wire to connect the circulator pump? over time the wire will heat up and the insulation might get soft and melt. If the wire from the control to the pump is in a flexible metal covering, the wire inside the covering may be failing.
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • jollyhombre
    jollyhombre Member Posts: 3
    Thanks this was helpful. The circulator actually heated up pretty high today. Swapped that out and everything is running now.

    Appreciate the help.