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@amaiale , take a pic from the end of the radiator so we can see what type and capacity are the sections it uses. Also how tall is it?

perfect application of a Thermostatic radiator valve. Turn up or down as you need or as your cat prefers. Just swap the valve, much easier than a new radiator.

Edit: Except that’s not the problem you are trying to solve! Less radiator not just less heat.
🤣

if the original installation was not designed properly, lack of adequate loops or well for example.
Maybe the load is larger than anticipated?

Or the installation was botched?

new replacement or repairs may not get what you expect

I would do some number crunching. A load calc as step 1

The 26-99 would easily support 3x what you have and is grossly oversized (though would modulate). Even the 15-58 will do nearly double what you have without issue. The Alpha 15-58 and two 3/4" Sentry zone valves would do a heck of a job here but if cost is of any concern, one UPS15-58 on each zone would be a great fit as well.

I typically run my loops 250ft in residential homes and use 32% glycol, and a single 15-58 starts to max out at about 14-15 loops. I do typically use the Alpha 26-99 with zone valves and/or actuators when it's 3 or more zones and 15+ loops, but something like yours would be two UPS 15-58 (if a budget build) or an Alpha 15-58 with two zone valves.

find a different contractor

Back in the day, before mod cons, CI boilers were commonly piped with 4 way motorized mix valves.

This valve both protects the boiler from low return, and provides the mix down temperature. Many of the Euro boilers offered this assembly. Tekmar, HBX are a few that still offer the valve, actuator, and controller.

\If return drops below acceptable temperature the valve modulates to protect it as priority.

Possibly a single circ will; work, depending on the loop requirements, gpm and head.

If not a two pump system was used with either a high pressure drop boiler, or high pressure drop radiant.

Buderus used to promote that "flexible cast iron" as being able to accept low return without damage? But flue gas condensation needs to be considered.

Price it with the components to use that boiler, or a combi.

Many here rave about simplicity and long life, inexpensive maintenance and parts of CI boilers.

The 4 way also provides outdoor reset.

Caleffi Idronics #7 talks about numerous mixing options for projects like yours. Hard to beat a 4 way.