You could use a simple switching relay.
I have heated with a wood boiler outside now for several years. I just recently installed an oil boiler in the system for when I want to be away or for if I can't tend the wood fire. I am heating 2 buildings from the same heat source be it oil or wood. It isn't working the way I would like it to and I need to know how I can make the thermostat start the circulator instead of the auquastat controlling the circulator. This would work a lot better for my needs. I think I just need to know how to change the wiring at the auquastat but I have no idea what I am doing with it and don't wish to make matters worse by just fooling around with the wiring and the settings. The auquastat is an older one but from what I have been reading it looks like they are all pretty much the same as the one I have. I am very rural and can't find anyone that seems to know how to set this up. I am hoping someone here can tell me how to hook up my wiring so that the thermostat itself controls the circulating pump and not the boiler. This would work much better for my application. Also there is a domestic hot water coil in the boiler but I do not need it nor will I need to ever use it so if need be it can be by-passed in the wiring or in the auquastat settings. Thanks in advance for any help you are able to give me.
Thanks John. Is there a way to just change the wiring around in the aquastat control box? The thermostat is 24 volts and the circulation pump is 110 volts and the auquastat has a transformer so I think it has to be done through there somehow no? I build furniture and I was a machinist by trade and have worked as a welder in the past but when it comes to electrical things I am lost I know very little about them.