Hot and cold shower

[readytow]

Recently upgraded to a 2006 Sunnybrook 31BWKS. When taking a shower, with a full and hot, hot water tank. The shower starts out hot, then, the water pump kicks on, and it goes very cold. Water pump turns off, gets hot again, water pump turns on, goes very cold.
The dealers service department has looked at it twice, they say all the valves in the water lines are open as they should be. They claim it is part of the water saving feature, that the pump does NOT run constantly when the shower is on. And also claim the hot and cold is because my shower head is not mixing the water properly. I replaced the shower head and still have the same issue.
Is this normal, and can someone please please please give me a clue as to what is going on?
Thanks!

[othertonka]

First, is this operating from the tank or on "City water" with the pump On? If on city water you don't need the pump ON. If operating from the tank I would check the outside shower faucet and make sure both hot and cold faucets are OFF. If they are left on and the shower head is turned off at the head itself, hot and cold water can mix through the valves and cause cold water at your inside shower. Let us know which way you are operating, from tank or city.

[newman_fulltime]

Are you running the pump while on city water