The machine runs but the water is weak, or it surges and drops rhythmically. Work down this list in order — the first three items account for most cases and cost nothing.
1. Air in the system
The commonest cause, and the easiest fix. An air pocket in the pump means it is compressing air instead of pushing water, which gives weak pressure and pulsing.
Fix: turn the machine off, leave the water on, and squeeze the trigger until water flows steadily with no spluttering. That can take thirty seconds. Then restart. This is also step six of the setup sequence, and skipping it is why so many machines seem weak on first use.
2. A blocked nozzle
A nozzle orifice is tiny and a grain of grit halves your pressure. Classic symptom: pressure was fine, then dropped suddenly.
Fix: swap to a different tip. If the problem goes away, the first tip is blocked. Clear it with the thin wire from your machine’s kit or a paperclip, pushing from the back — never force anything into the orifice from the front, which deforms it permanently.
3. A clogged inlet filter or starved supply
The pump can only push what reaches it. Check, in this order: the inlet filter (rinse it), the garden hose for kinks, the tap fully open, and the hose diameter — a narrow hose chokes a thirsty machine.
Test your supply: time a 5-gallon bucket from the tap. Under 60 seconds is comfortable for any machine on this site. Much slower and your real flow is below the machine’s rating, which no amount of fiddling with the machine will fix.
4. The wrong nozzle size for the machine
Nozzles are sized by orifice to a flow rate. A tip rated 2.5 GPM on a 1.2 GPM machine is too large: water passes through without building pressure, so the machine feels weak even though nothing is broken.
Fix: buy a tip set whose stated rating matches your machine’s GPM — nozzle sets by flow rating. This catches a lot of people who bought a generic set.
5. A leak somewhere in the line
Walk the whole run with the machine on: machine outlet, hose fittings, gun inlet, wand joint. A weeping fitting is losing pressure, and the usual cause is a perished O-ring rather than a wrong-size fitting.
Fix: replace the O-ring, and use PTFE tape on threaded joints. Fitting sizes and the M22-14 versus M22-15 trap are in the quick connect guide.
6. The hose is kinked, too long, or damaged
A kink is a restriction. An over-long run costs real pressure. A bulge in the hose is a failure in progress.
Fix: straighten it, shorten it, or replace it. Fifty feet is a reasonable maximum for a homeowner machine — choosing a hose.
7. The unloader valve is stuck
The unloader diverts water back through the pump when the trigger is closed. If it sticks, it can stay in bypass and never build pressure, or cause a hard surge-and-drop cycle.
Fix: sometimes freed by running the machine and squeezing the trigger repeatedly, which cycles the valve. On many consumer machines this is not serviceable, and it is the point at which repair economics start to favor replacement.
8. Worn pump valves or seals
The end of the road, and usually caused by one of two things: grit from the supply chewing the valves, or having run the pump dry at some point.
Fix: rarely economic on a consumer electric machine, where pumps are sealed. On a gas machine with a serviceable pump, a rebuild kit may be worthwhile. Prevention is the whole strategy: an inlet filter and never running it dry.
If the symptom is specifically pulsing
Pulsing is a narrower set of causes: air in the system (item 1), a partially blocked nozzle (item 2), a starved supply (item 3), or a sticking unloader (item 7). Work those four first.
And if the detergent is what is not working rather than the pressure, that is a different page — soap injector not working.
