Water Coming out of Shower head Cold But just right at tub before pulling diverter

Delta 1700 series

How cold is cold? Is this shower on an outside wall? Could it be that it's cooling off a bit in the wall on its way to the showerhead (wouldn't much unless the wall cavity was totally uninsulated and breezy I would think)? Which cartridge do you have in that? Single handle, volume control, or thermostatically controlled?

It's not unusual for it to start out cold but it should come up to temp quickly. If not, what Jim said would apply.

Jim
This is a Delta 1700 series where the temperature is all part of one dial. Had the unit installed for about 7 years no problem. the water comes out of the tub spout at whatever temperature you elect. When i pull up on the diverter, the water then comes out of the shower. however, very cold. even if i elect to have the water come out of the tub spout as hot as possible, once i hit the diverter it comes out of the shower cold. Delta tech told me they never heard of this? Wall is well insulated and it was almost 70 here yesterday.

The "logical" answer, although not immediately explainable, is that it is related to internal pressure change when shifting to shower, and therefore the issue may be related to the pressure balance spool. Simply install a new cartridge, and if the problem persists, call in an excorsist.

Jimbo is being quite logical... On the 1700 series, the tub spout has a larger port for fast filling with very little back pressure. The shower port is smaller plus the vertical rise and flow restriction in the shower head would result in more back pressure on the balance spool.