Getting a low flow? Check for any pipe kinks
QHow can I improve the very slow hot water flow on my Elysian 27? Install a higher pressured pump? De-scale the (original) calorifier?
ATypical calorifier scale would not affect the hot flow rate because it would be on the outside of the heating coil, but would make it slow to heat.
It is probably best not to fit a higher pressure pump unless you can establish the opening pressure of the Pressure Relief Valve ( PRV). Your water pump should be set to shut down at least 0.5 bar lower then the PRV.
If there is a non-return valve close to the calorifier cold water inlet, check this is not rusted or scaled up and the plunger/flap moves freely. Check no elbows, bends or T-fittings are blocked with scale or rust, and any hoses or plastic pipes aren’t kinked or squashed. Make sure no hidden valves are partially closed.
If you’ve checked all these then, although this is a small boat, my guess is that the total pipe run for the hot water is at least twice as long as the cold, causing more friction, which translates to a lower flow. Consider increasing pipe size: I would want to see at least 15mm internal diameter; possibly 22mm for pump to calorifier.