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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Taco SR502 2 zone switching relay --wiring

Customer Question

I have a Taco SR502 2 zone switching relay
--wiring configured as Cold start boiler application
And a 501 switching relay
2 zones
1) heat
2) domestic hot water (side arm)
Issue no hot water
Boiler won't start
SR502 is powered up
Shows call from hot water stat
It seems the problems is at the SR502 terminals X1 and X2 no voltage. Seems there should always be 28V here
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

The XX end switch terminals are dry contacts (no voltage). They should however be closed when there is a call for heat. So you need to test continuity across those terminals when you have a call for heat and no response from the boiler (assuming the boiler isn't up to limit temp).