2 circuit boiler system. One pump motor will not stop running.

My friend has a boiler with two circuits to heat each half of his house. One of them seems to run non stop and overheats half of the house even after the thermostat is disconnected. The other motor turns on and off as it should and heats the other half of the house properly. The only way to turn this pump off has been to remove the wire nut from the hot wire in the actual motor.
Aquastat is new. Boiler holds at about 20psi and 180 degrees.
Circuits each have their own pump/motor so there are no zone valves. Transformer/control things on adjacent wall have terminals for R C G W Y. Transformer/control paired with properly running motor has 24v at G when motor is running only.
Motor that runs continuously runs whether there are 24v supplied to G or not. Disconnecting wires from R on this control did not stop the motor from running.
Please help =)

 

Model number of these 'things' please? Sounds like they are R8285 controls?

Sounds to me like a 'stuck relay'. Probably can pull the plug-in relay and put in a new one in about ten seconds... if you knew what relay and where to get it.

 

Looks like this. Has the same terminal lettering as a thermostat. R to G makes the pump run, except the one that keeps running, which runs anyways. Haven't been back to the house since they had this problem.

 

I'm working in the field right now but I've only been doing it less than a year and this is my first real experience with a boiler issue. I'm sure I can go and get the part from a supplier I'm just not even sure what these are called exactly. It would make sense that this is the problem though. Thermostat and aquastat have both been replaced for one reason or another already so that pretty much leaves this. You mentioned it's a "plug in." Not familiar with them but sounds great if so lol... Thank you for the reply.

 

Yes, that control is an R8285 'family'. There are a few manufacturers that make very similar and functionally equivalent controls, but Honeywell seems to dominate the market. They call these 'fan control centers', but they can be used for any number of applications, in this case to run a circ and fire the boiler.

The device on the bottom, below the transformer is a 'relay', aka 'contactor'. It is a plug-in. That wire 'bail' across the top holds the relay in. To remove it, slide the bail to the side and pull the relay out. Read the label on the side... it is probably a Honeywell R8222 but like the control itself, there are numerous manufacturers of that part, and it should be available locally at a well stocked heating supply. They should have a 'cross reference' available to get you the right one.

Should cost about $20 or so.

99.9% certain that's the problem.