Shower water pressure goes down during shower and then returns.
A single lever diverter.
No other water pressure issues.
Third floor of a 3 decker house in Boston

Hey fellow Bostonian.

Is this problem new?

You said you are in a multi. Family (3rd floor)... if pressure drops and then returns is it possible that someone in building is using the water at a toilet, a sink, a dishwasher, a washing machine, etc.?

If this is the case, all OK as long as there is a corresponding drop in pressure in hot and cold and you are not getting burned. Let me know.

The problem is new brought to me by a new tenant.
I am in contact with the previouse tenant and he has told me he had no such problem.
The shower diverter is a single lever. I believe a Simmons. As turned counterclockwise increases water flow and increase in water temperature.
I have replaced the washers in the stem.
The lever works to transfer water flow from shower to tub spout and viseverser. I have just found out by calling the tenant that they correct the problem by turning this lever to direct the water to the tub. The water flow returns and then they turn the lever back to direct the water to the shower and the water flow returns.