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Wirsbo SYSTEMPro 311 Bad Switch/Relay?

jdperlow Member Posts: 3
I own a home with Wirsbo SystemPro 311. I'm observing an (increasingly) intermittent failure condition where the thermostats are calling for heat, but the entire system is cold because the boiler is not turning on. I noticed that when it gets into this condition, the flame icon is illuminated (indicating it's activating the boiler), but the relay is not closing the boiler switch between 15/16 (based on volt-meter reading). Power cycling the controller sometimes fixes the problem. The problem eventually also resolves on its own (but can take multiple hours).

Does this indicate that the relay is failing or are there any legitimate reasons this should occur? If this is a broken relay, is this serviceable or does the unit need to be replaced?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,501
    edited March 2023
    Those screw terminals actually are plugs. Have you tried to unplug that 15/16 plug then plug it back in? Other than that, if the relay contacts are defective, I do not think that is a field replaceable relay.. It is time for a new control.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • 109A_5
    109A_5 Member Posts: 1,336
    Hello @jdperlow,
    If it is actually a relay problem (sounds like it could be), relays like that are usually inexpensive and easy to change if you have the tools and skills. Also it could just be a bad solder joint, considering the age I believe it is and it is quite common to see solder joints fail at relays. Either way you would need an Electronics Technician to do the repair or someone that can do that type of work.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System