Start by comparing
The fastest way to narrow down low pressure is to compare. Is it only the shower, or the whole bathroom, or the whole house? Is it weak on both hot and cold, or just one side? Did it change suddenly or fade over years?
A sudden drop in one shower usually points to something local, like a clogged head or a failed cartridge. A slow decline across the house in an older Fullerton home can point to galvanized supply pipe narrowing inside with corrosion.
Symptom and likely cause
| What you see | Likely cause |
|---|---|
| Weak only at the shower head, spout is strong | Clogged head, flow restrictor or worn diverter |
| Weak at both head and spout | Cartridge, valve stops partly closed, or supply |
| Only hot is weak | Hot side of the valve, or the water heater and its connections |
| Whole house is weak | Main shutoff partly closed, pressure regulator, or supply pipe |
| Slowly worse over years, older house | Corrosion inside galvanized supply pipe |
| Dropped right after other plumbing work | Debris lodged in the cartridge or head |
Checks you can do
- Remove the head.Run the shower with the head off for a moment. If flow from the arm is strong, the head is the problem.
- Test the spout.On a tub-shower, compare spout flow to head flow. Strong spout, weak head points to the diverter or head.
- Compare hot and cold.Run each alone at a nearby sink and at the shower to see if one side is restricted.
- Check the main.Make sure the house main shutoff is fully open, especially after any recent repair.
What a plumber may check
- The cartridge and valve for scale or debris
- Whether the valve stops are fully open
- The diverter on a tub-shower
- The pressure regulator, if the house has one
- The condition and material of the supply pipe to the bathroom
What to ask
- Is this a fixture problem or a supply problem?
- Can you measure my house water pressure?
- If the pipes are galvanized, how much of the house is affected?
- What is the smallest fix that would solve this?
Common questions
Will a high-pressure shower head fix weak flow?
It may feel stronger by narrowing the spray, but it won't fix a clogged cartridge or restricted pipe.
Why did pressure drop after a cartridge change?
Debris from the pipes can lodge in a new cartridge, or the stops may not have been reopened fully. Both are quick to check.
Does low pressure mean I need repiping?
Not necessarily. Rule out the head, cartridge, diverter and shutoffs first. Repiping is a bigger decision for widespread pipe problems.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.