It's cycling because the boiler is massively over sized for the amount of radiated floor area. I suspect the boiler may not be properly piped either. The only way around this is going to be to install a buffer tank sized to the load. I see this all the time with mod-con boilers. The staple up radiant can't shed heat fast enough so the delta T is way too narrow. In short, the burner heats up way faster than the floor can shed it.