I have a Taco ZVC403 zone valve control box. I have 3 zones each having their own thermostat. When a zone calls for heat there is a “LOUD” buzzing noise and I believe it is coming from the zone valve box. What would cause this? The strange thing is it doesn’t happen all the time. I’ve been shutting the power switch (electric) off to the boiler when it does happen. Any help would be greatly appreciated. Thank you in advance. Peter
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