The thermostat on the boiler should always be set to 70 - 75C. Especially with UFH as you want a ΔT of 11C. My boiler is a condensing HE boiler so it is also more critical to keep at this temperature is ensure that it is in condensing mode as much as possible.
A very good option is to install a modulating circulating pump such as the Grundfos Alpha pump. Once installed, you open all circuits including the hw, set this to be the template setting and as circuits close, the pump will modulate back to suit. It ensures a ΔT is maintained which is critical with ufh.
The pipe stat on the UFH is only there to protect the concrete slab from overheating and cracking. This should be set to approx 55C and certainly no more than 60C. This stat will turn off the UFH pump at temperatures above this so not to pump higher temps through the slab which could lead to cracking. The UFH heating circuit should generally be at a temperature of 45C with a return temp of 34C. If you have very different temps, then your flow regulators are incorrectly set. If you have lower temps then you need to increase the flow rate on each circuit. This is not a job for the untrained.
If you have your system zoned, and I mean with motorized valves on each circuit including the hw, then I would try to put on the hw circuit on the different time to the ufh. It will heat up quicker and take nothing from the ufh. If it is not zoned, do so but get somebody who is able to do so correctly. UFH often operates at 24v and relays, etc. must be used to link the various controls. Depending on when you home was built, you should qualify for the SEAI Heating Control Upgrade grant as you will probably not have time and temperature control on your hw circuit and each zone probably cannot be completely isolated in that if downstairs is on and one room upstairs wants heat, it will get it even though upstairs is in set back.
You may also have an ICV (Injector Control Valve) and this will be set to the desired flow temperature. This allows higher flow temps to be added to the return temps. An ICV looks similar to a TRV but on a pipe.