What should I do (look for) to find out why the cold side of my shower faucet has developed VERY low water pressure, but not the hot side.

The sink faucet in that same bathroom is fine on both sides. All other faucets in the house are fine on both sides.

I don't have a hot water tank (tankless oil-fired boiler).

Thanks

Vermont

speedball1

Hi Vermont, Florida calling,

Before we can help we must know the brand name of the shower valve and about how old it is. Also the type, one handle or two knobs? Happen all of a sudden or come on gradually? Answer and we'll get back to you ASAP. Tom

lowcoldwaterpressure

Delta brand

one-knob handle

it may be 25 years old - that's when the house was built

the problem seemed to appear one day - about three weeks ago

it has gotten worse slowly - now the cold side is barely more than a drip

speedball1

You're going to have to open up the valve and pull out the parts right down through the seat and springs, #7 on the diagram. Inspect the seats and springs and replace if necessary. Now turn on the cold water and flush out the cold water supply. You should have a full stream coming out of the open valve. If not check further back down the cold water line for a blockage in the cold water branch. Note: The valve may show parts that yours dosn't have but the basic valve's the same. Good luck, Tom