Burnham boiler mid century house with radiant heat floor

[Bail]

I had a quick question about boiler water temperature I have adjusted the temperature output dial to be 220° but after running the boiler for about two hour the water only goes up to about 120° and seems to stay there.The house is 1400 ft.² and has copper pipe in the slab also all zone are open looks like there’s ten of them. my question is I should in theory be able to get that temperature up to at least 150° my other question is the sensor for that temperature on the supply side or the return side? When I feel the return it’s warm and the supply is hot. Would replacing expansion tank help its probably 20 years old