diff --git a/pybop/models/lithium_ion/utils.py b/pybop/models/lithium_ion/utils.py
index be95bd80d..6448306b0 100644
--- a/pybop/models/lithium_ion/utils.py
+++ b/pybop/models/lithium_ion/utils.py
@@ -3,6 +3,7 @@
 
 import numpy as np
 from pybamm import Interpolant as PybammInterpolant
+from pybamm import Symbol
 from scipy import interpolate
 
 if TYPE_CHECKING:
@@ -51,7 +52,7 @@ def __init__(
     ):
         self.x = np.asarray(x)
         self.y = np.asarray(y)
-        self.name = name
+        self.name = name if name is None else name.replace(" ", "_")
         self.kind = kind or "linear"
         self._interp_func = self._create_interpolant(bounds_error, fill_value, axis)
 
@@ -82,14 +83,15 @@ def __call__(self, x: float | np.ndarray):
         float, array_like, or pybamm.Interpolant
             Interpolated values or PyBaMM interpolant object.
         """
-        try:
-            # Try numeric evaluation first
-            return self._interp_func(x)
-        except Exception:
-            # Fall back to PyBaMM interpolant for symbolic evaluation
+        if isinstance(x, Symbol):  # symbolic evaluation
             return PybammInterpolant(
                 self.x, self.y, x, name=self.name, interpolator=self.kind
             )
+        else:  # numeric evaluation
+            return self._interp_func(x)
+
+    def __repr__(self):
+        return f"{self.name}, {self.kind} interpolant"
 
 
 class InverseOCV:
@@ -116,11 +118,13 @@ def __init__(
         self.optimiser = optimiser or SciPyMinimize
         self.optimiser_options = optimiser_options or self.optimiser.default_options()
 
-        parameters = Parameters({"Root": Parameter(initial_value=0.5, bounds=[0, 1])})
+        self.parameters = Parameters(
+            {"Root": Parameter(initial_value=0.5, bounds=[0, 1])}
+        )
 
         # Set up a root-finding cost function
         class OCVRoot(BaseSimulator):
-            def __init__(self, ocv_value: float):
+            def __init__(self, parameters: Parameters, ocv_value: float):
                 super().__init__(parameters=parameters)
                 self.ocv_value = ocv_value
 
@@ -153,7 +157,7 @@ def __call__(self, ocv_value: float) -> float:
         float
             The stoichiometry corresponding to the open-circuit voltage value.
         """
-        problem = Problem(self.ocv_root(ocv_value), self.cost)
+        problem = Problem(self.ocv_root(self.parameters, ocv_value), self.cost)
         optim = self.optimiser(problem, options=self.optimiser_options)
         result = optim.run()
         return result.best_inputs["Root"]
diff --git a/pybop/parameters/distributions.py b/pybop/parameters/distributions.py
index 0b8ae4c8e..2572555b2 100644
--- a/pybop/parameters/distributions.py
+++ b/pybop/parameters/distributions.py
@@ -431,7 +431,7 @@ def __init__(
         self.initial_value = (
             None
             if initial_value is None
-            else float(np.minimum(np.maximum(initial_value, lower), upper))
+            else float(np.clip(initial_value, lower, upper))
         )
 
     def support(self) -> tuple[float]: