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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 22017
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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Have a two year old Purepro brand Nat gas boiler, the gas

Customer Question

Have a two year old Purepro brand Nat gas boiler , the gas valve is functioning fine but intermittently makes a very high speed loud rattle that you can here through the whole house. The valve still allows gas to the main burners while this is happening .only happens about twice a day with out regard to temperature .almost sounds like the valve wants to shut and stay open at the same time but the rattle is very fast. It is definitely NOT hydronic system air bled everything and when it happens you can hear it's coming right from that valve
Submitted: 2 years ago.
Category: HVAC
Expert:  Rick replied 2 years 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.
A rattling noise is unusual from a gas valve but noise descriptions are notoriously subjective. If you're sure it's coming from the gas valve and not the system piping then you need to check for 24 vac at the valve. If you have 24 vac at the valve when the noise occurs then you either have a bad gas valve or a bad connection between the valve and the control. Of course if you have a bad connection you're probably going to see something less than 24 volts.

Customer: replied 2 years ago.
Have 24 to 28 volts when it's NOT making the noise,when it is making noise voltage jumps all over from 1 to 3 to everything but not more than 10 or so, checked all connections up to main control everything is clean an tight
Expert:  Rick replied 2 years ago.

If you're sure all the connections are good then you probably have an issue with the ignition control. What do you have for an ignition control? Is it a Honeywell S86?

Expert:  Rick replied 2 years ago.

I just checked the PurePro specs and it looks like most have a Honeywell S86 so you want to probe across MV & MV/PV. If the voltage is constant then you have a bad lead to the gas valve. If it's not constant probe across 24v & 24v GND. If you have steady voltage there then the control is suspect. If you don't have steady voltage there then you need to follow the circuit back to each component to see where the voltage is dropping out

Customer: replied 2 years ago.
Have constant power on MV and MV Pv. 24 volts , wires look really good and connections all the way to the gas valve
Expert:  Rick replied 2 years ago.

If 24 v is constant at MV & MV/PV but not at the same terminals on the gas valve then the only explanation is defective leads from the control to the gas valve