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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Controller for CG-A maybe malfunctioning at times. My guess

Customer Question

controller for CG-A maybe malfunctioning at times. My guess is that a relay is sticking on the L8148. Why should there be a voltage between TV and T with all wires off?
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: a couple of days, All wires to tacos are disconnected and I can get it to fire ok with any green/white pair from the valves and almost normal for a while.
JA: Do you plan on doing the work yourself?
Customer: WOrst case scenario is to replace the controller and may need a plumber. But first I would like to know where that 27VAC between T and TV is coming from with no wires hooked to them
JA: Anything else we should know to help you best?
Customer: The furnace is a New Yorker Class CG-A series with a small pump and the vent damper
JA: Did you check the furnace's filters?
Customer: no,
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 7 months 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.

It sounds like you have Taco zone valves. If so that's where the voltage comes from. When the zone valves close they also close an end switch which calls in the pump and the burner. If you jump T & TV and the boiler finctions normally then the problem is not with the L8148.

Customer: replied 7 months ago.
not possible, all connections to TV and T are out. The 24VAC from transformer go to thermostat and come back to pin 1 of the taco but the TV-T is disconnected from anything and reading 27.4 volts. Those should be contacts
Expert:  Rick replied 7 months ago.

Your not looking at this the right way. I'll help you diagnose this issue if you're willing to follow my advice. I have 40+ years experience installing and servicing hot water heating systems.

Customer: replied 7 months ago.
Normal operation uses when 28V shows up from thermostat to pin 1 of valve and closes the 2-3 contacts that go to the controller. I disconnected T and TV at the controller so there is no wires coming to the controller from the valves or from anywhere. 27V at T TV must be internal to the controller
Customer: replied 7 months ago.
jumping T-TV starts the furnace but that is what the problem is. It does not work all the time. That tells me that something else in the cycle is stopping the start. It is suppossed to wait for the damper to open then fire. A few cycles of on and off, with T-TV shorted will eventually work normally and then all works for a while till it fails again
Customer: replied 7 months ago.
that is why I asked the original question. Where is that 27VAC internal to the controller come from?
Customer: replied 7 months ago.
It could be normal, (I dont know). That is, the T TV contacts could be routing 27 VAC elsewhere. I thought they were SPST relay contacts that the controller uses. But I thought they were just routing the 28V form the thermostat to a controller transformer primary.
Customer: replied 7 months ago.
If it is normal, that is, if the controller is routing its own 27VAC to that primary thru the TV-T contacts, then the intermittent problem could be the damper gets stuck. I think the sequence, according to the manual is damper then furnace.