If you use a shower pump (15mm fittings) to pump a whole house are you asking for trouble?

someone has installed a shower pump with 15mm fittings even though all the pipework is 22mm - I suspect the whole house pump has been replaced with a shower pump at some time and now the pump gets air locked after heavy use . Is there a difference in design between the two ? and woyuld you expect these problems using a shower only pump for a whole house. Any advice really appreciated