Work down this list in order. The first item is the cause in most cases, costs nothing, and takes ten seconds.
1. The wrong nozzle is fitted
A soap injector is a venturi: it only generates suction when the water downstream can leave freely. A high-pressure tip creates back-pressure that cancels the suction entirely.
Fit the black 65-degree soap tip. If you do not have one, that is the entire problem and a seven-pack costs a few dollars. On machines with a fixed adjustable wand, pull the lance forward or twist to the low-pressure position — check your manual for which.
This accounts for most reports. Mechanism: how soap injectors work.
2. The detergent is too thick
An injector can only draw a thin liquid. Undiluted gel concentrates, cold thick soap, and anything syrupy will not move through a narrow pickup tube.
Dilute it as the label directs, and use warm water to mix — cold thick concentrate is a common cause on the first use of a new bottle. Ratios: mix ratios.
3. The pickup filter or tube is blocked
There is a small filter on the end of the pickup tube. Dried detergent, and especially dried bleach residue, blocks it.
Pull the tube out, rinse the filter, and check the tube is clear by blowing through it. Also check it is not kinked, and that it actually reaches the bottom of the bucket — a tube sitting above the liquid level draws air.
4. Air is getting in
A venturi that draws air instead of liquid does nothing. Check: the tube is fully pushed onto its barb, there is no split in the tube near the fitting, the bucket has enough liquid, and any O-ring at the injector port is present and intact.
A tube that has gone hard and no longer seals on the barb is a common and cheap failure.
5. The check valve is stuck
Inside the injector is a small ball or poppet check valve that stops water flowing back into your detergent. It sticks when residue dries around it, which is why flushing matters.
Some injectors come apart; many do not. Soaking the injector body in warm water for an hour sometimes frees it. If not, this is a replacement — they are not expensive.
6. Your flow is too low
The venturi needs enough water moving through it to create suction. If the machine is already underperforming — weak pressure, pulsing — the injector will be the first thing to stop working.
Check the inlet filter, the garden hose for kinks, and your supply tap. If the machine is generally weak, fix that first: won’t build pressure.
7. The tank selector valve (two-tank machines)
If your machine has two detergent tanks, there is a selector valve, and it may be set between positions or to the tank you did not fill. Trivial, and worth checking before dismantling anything.
If it draws but nothing seems to happen on the wall
That is not an injector fault. The injector dilutes your bucket mix considerably on the way through, so what lands is weaker than what you mixed. Mix stronger in the bucket, and give it real dwell time — five to ten minutes, never drying.
For anything delicate or precise, a hand pump sprayer applies exactly the mix you made and removes the whole question.
Preventing it next time
Flush with clean water after every use: pickup tube in a bucket of water, soap tip fitted, thirty seconds. This is the entire maintenance requirement, and skipping it after a bleach mix is how check valves die — see bleach and pressure washers and the maintenance checklist.
