If there is no drain valve at the radiator you can drain the system at the drain valve on the boiler
headboard
Radiator drain plug sizes vary from vehicle to vehicle. Some radiators have a drain plug and others have a petcock.
Not all radiators have petcocks. Simply disconnect the bottom hose to drain.
Contact a heating contractor and ask him for quote!!
Gently remove the lower radiator hose from the radiator and use a wide shallow drain pan to catch the coolant.
there should be a drain plug on all radiators on the bottom of radiator on either bottom corner or possibly in middle on bottom
The hot water may be turned off to them or the valves could be clogged. Rust and sediment build up over time and stop the flow.
Naturally on all radiators, the drain-valve is at the very bottom if you look under the actual radiator for a butterfly-like valve with a hole inside it for the water to come out.
Some radiators dont have a drain plug and the ones that do is hard to reach. Its easier and quicker to remove the lower radiator hose. (passenger side,below the engine)
A baseboard can be 3/4 inches
Most radiators on these new models do not have drain plugs, especially if it's an aftermarket taiwanese radiator. If you have not found one after looking for it, your best bet is to drain it by removing the hose that leads to the water pump.
Radiators produce heat.