Insufficient pump flow would be another reason why it couldn't deliver enough heat, and that would show up as a larger difference in temp between outgoing & incoming water.
It's also possible that it's outdoor-reset was programmed to the wrong curve, or it's outdoor temp sensor is mis-installed/defective giving a too-high reading, lowering the output temp of the boiler.
Sizing a hydronic boiler by measuring the radiation size is just as inaccurate as doing it by square feet of living space. But once the heat load is known by a proper heat loss calculation you'd need to measure the radiation to determine the peak water temperature, and select the outdoor reset curve accordingly.
At full fire with 180F outgoing water the best the Purefire 110 is going to deliver is ~ 85% efficiency, which would mean with a 110K input you'd get 93-94K out. ( At lower output temps-or more accurately, lower RETURN temps, that rises slowly until you get down to ~140F out below which the efficiency climbs quickly into the 90s.) Mind you, 93K still 3X the heat load my ~2200 square foot 1920s home with storm windows over & double-hung windows has at 4F. You'd have to be practically un-insulated &/or have a window flung wide open to have a true heat load over 90KBTU/hr at 4F in a mid-sized house, but I suppose anything is possible.
Still, if it held the line at 61F you only need a ~10% improvement in the thermal & pressure envelope of the house to make it work. That could be as simple as fixing any major air leaks do you have any open fireplace flues? Mail slots? Recessed lights cutting into the attic? Assuming it's a full basement, is the foundation sill & band joist all cob-webby (a sign of air leakage.) Foundation sills & band joists are the single largest most commonly overlooked infiltration point- it's HUGE! How about door sweeps & weather stripping on exterior doors?
Air sealing is your single-most cost effective improvement- find an insulation contractor who specisalizes in it after you've nailed down the most obvious stuff. Treat all the big holes first, but then concentrate on leaks into the attic, and leaks into the basment. The stack-effect is a huge driver of air infiltration- if you fix it at both the top and at the bottom, you can get away with a lot of leakage in-between (but fix those anyway.)
If you have single-pane windows, storm windows (exterior or interior) are cost effective, for far less cash outlay than even bottom-of-the-line replacement windows, and if the original windows are reasonably tight, with storms they'll even OUT PERFORM bottom of the line replacement windows.
A lot of 1950s houses had R8 "econobatt" insulation in 2x4 studwalls, leaving about a 2" gap of empty space inside the wall cavites. Better ones had R11 full-depth batts, but over time those can sag/fall leaving gaps & voids in the insulation. In almost all timber-frame construction it's possible to retrofit blown cellulose into cavites without completely ripping the house apart, and it's well worth it from both a comfort and economic point of view. You could blow rock wool or fiberglass in there as well, but cellulose does a measurably better job of slowing down air movement through the walls, and it usually about the same cost or even somewhat cheaper. Ideally they would be able to "dense-pack" the material to 3lbs+ per cubic foot density, at which point it will have reduce the air flow potential by ~98% below that of 1950s style R11 batts. If yours has R8 econobatts it would be great news, since it's easier/cheaper retrofit blown insulation into a partially empty wall cavity that a "dense-packing" tube fits into more readily. Dense-packed you'd be in the ~ R13 range, but unlike low-density batts, it would stil PERFORM at R13 when it's 0F out, whereas R11 batts lose nearly half their R-value at temps that low due to convection currents in the insulation itself.